Skip to content

G
Gpdb

Greenplum / Gpdb

通知 7
Star 1
Fork 0
G
Gpdb

体验新版 GitCode，发现更多精彩内容 >>

切换分支/标签
查找文件 普通视图历史永久链接Permalink
FAQ.html 49.1 KB
Newer Older
B
Update FAQ.  
Bruce Momjian 已提交
1 
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
2
B
Update FAQ.  
Bruce Momjian 已提交
3 4 5 6 7 8 9 
<HTML>
  <HEAD>
    <META name="generator" content="HTML Tidy, see www.w3.org">

    <TITLE>PostgreSQL FAQ</TITLE>
  </HEAD>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
10 
  <BODY bgcolor="#FFFFFF" text="#000000" link="#FF0000" vlink="#A00000" alink="#0000FF">
B
Update FAQ.  
Bruce Momjian 已提交
11 12 13 14 
    <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>

    <P>Last updated: Tue Oct 17 00:21:20 EDT 2000</P>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
15 
    <P>Current maintainer: Bruce Momjian (<A href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
B
Update FAQ.  
Bruce Momjian 已提交
16 17 
    </P>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
18 
    <P>The most recent version of this document can be viewed at <A href="http://www.Postgresql.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P>
B
Update FAQ.  
Bruce Momjian 已提交
19
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
20 
    <P>Platform-specific questions are answered at <A href="http://www.PostgreSQL.org/docs/">http://www.PostgreSQL.org/docs/</A>.</P>
B
Update FAQ.  
Bruce Momjian 已提交
21 22 23 24 25 26 27 
    <HR>

    <CENTER>
      <H2>General Questions</H2>
    </CENTER>
    <A href="#1.1">1.1</A>) What is PostgreSQL?<BR>
     <A href="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
28 
     <A href="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
29 30 31 32 33 
     <A href="#1.4">1.4</A>) What non-unix ports are available?<BR>
     <A href="#1.5">1.5</A>) Where can I get PostgreSQL?<BR>
     <A href="#1.6">1.6</A>) Where can I get support?<BR>
     <A href="#1.7">1.7</A>) What is the latest release?<BR>
     <A href="#1.8">1.8</A>) What documentation is available?<BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
34 
     <A href="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
35 36 37 38 
     <A href="#1.10">1.10</A>) How can I learn SQL?<BR>
     <A href="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR>
     <A href="#1.12">1.12</A>) How do I join the development team?<BR>
     <A href="#1.13">1.13</A>) How do I submit a bug report?<BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
39 
     <A href="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
40 41 42 43 44 45 
     

    <CENTER>
      <H2>User Client Questions</H2>
    </CENTER>
    <A href="#2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?<BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
46 47 48 
     <A href="#2.2">2.2</A>) What tools are available for hooking PostgreSQL to Web pages?<BR>
     <A href="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?<BR>
     <A href="#2.4">2.4</A>) What languages are available to communicate with PostgreSQL?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
49 50 51 52 53 
     

    <CENTER>
      <H2>Administrative Questions</H2>
    </CENTER>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
54 55 56 57 58 59 60 61 62 63 64 
    <A href="#3.1">3.1</A>) How do I install PostgreSQL somewhere other than <I>/usr/local/pgsql?</I><BR>
     <A href="#3.2">3.2</A>) When I start the <I>postmaster</I>, I get a <I>Bad System Call</I> or core dumped message. Why?<BR>
     <A href="#3.3">3.3</A>) When I try to start the <I>postmaster</I>, I get <I>IpcMemoryCreate</I> errors. Why?<BR>
     <A href="#3.4">3.4</A>) When I try to start the <I>postmaster</I>, I get <I>IpcSemaphoreCreate</I> errors. Why?<BR>
     <A href="#3.5">3.5</A>) How do I prevent other hosts from accessing my PostgreSQL database?<BR>
     <A href="#3.6">3.6</A>) Why can't I connect to my database from another machine?<BR>
     <A href="#3.7">3.7</A>) All my servers crash under concurrent table access. Why?<BR>
     <A href="#3.8">3.8</A>) How do I tune the database engine for better performance?<BR>
     <A href="#3.9">3.9</A>) What debugging features are available?<BR>
     <A href="#3.10">3.10</A>) I get <I>"Sorry, too many clients"</I> when trying to connect. Why?<BR>
     <A href="#3.11">3.11</A>) What are the <I>pg_sorttempNNN.NN</I> files in my database directory?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
65 66 67 68 69 
     

    <CENTER>
      <H2>Operational Questions</H2>
    </CENTER>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
70 71 72 73 74 75 76 77 78 79 
    <A href="#4.1">4.1</A>) Why is the system confused about commas, decimal points, and date formats.<BR>
     <A href="#4.2">4.2</A>) What is the exact difference between binary cursors and normal cursors?<BR>
     <A href="#4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?<BR>
     <A href="#4.4">4.4</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR>
     <A href="#4.5">4.5</A>) How do you remove a column from a table?<BR>
     <A href="#4.6">4.6</A>) What is the maximum size for a row, table, database?<BR>
     <A href="#4.7">4.7</A>) How much database disk space is required to store data from a typical text file?<BR>
     <A href="#4.8">4.8</A>) How do I find out what indices or operations are defined in the database?<BR>
     <A href="#4.9">4.9</A>) My queries are slow or don't make use of the indexes. Why?<BR>
     <A href="#4.10">4.10</A>) How do I see how the query optimizer is evaluating my query?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
80 81 
     <A href="#4.11">4.11</A>) What is an R-tree index?<BR>
     <A href="#4.12">4.12</A>) What is Genetic Query Optimization?<BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
82 83 84 85 86 87 88 89 90 91 92 93 94 
     <A href="#4.13">4.13</A>) How do I do regular expression searches and case-insensitive regular expression searches?<BR>
     <A href="#4.14">4.14</A>) In a query, how do I detect if a field is NULL?<BR>
     <A href="#4.15">4.15</A>) What is the difference between the various character types?<BR>
     <A href="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
     <A href="#4.16.2">4.16.2</A>) How do I get the value of a <SMALL>SERIAL</SMALL> insert?<BR>
     <A href="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?<BR>
     <A href="#4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a <SMALL>TID</SMALL>?<BR>
     <A href="#4.18">4.18</A>) What is the meaning of some of the terms used in PostgreSQL?<BR>
     <A href="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc failure: memory exhausted?"</I><BR>
     <A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I am running? <BR>
     <A href="#4.21">4.21</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR>
     <A href="#4.22">4.22</A>) How do I create a column that will default to the current time?<BR>
     <A href="#4.23">4.23</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
95 96 97 98 99 100 
     <A href="#4.24">4.24</A>) How do I do an <I>outer</I> join?<BR>
     

    <CENTER>
      <H2>Extending PostgreSQL</H2>
    </CENTER>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
101 102 103 104 105 
    <A href="#5.1">5.1</A>) I wrote a user-defined function. When I run it in <I>psql,</I> why does it dump core?<BR>
     <A href="#5.2">5.2</A>) What does the message <I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?<BR>
     <A href="#5.3">5.3</A>) How can I contribute some nifty new types and functions to PostgreSQL?<BR>
     <A href="#5.4">5.4</A>) How do I write a C function to return a tuple?<BR>
     <A href="#5.5">5.5</A>) I have changed a source file. Why does the recompile not see the change?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
106 107 108 109 110 111 112 113 114 
     
    <HR>

    <CENTER>
      <H2>General Questions</H2>
    </CENTER>

    <H4><A name="1.1">1.1</A>) What is PostgreSQL?</H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
115 116 117 118 119 120 121 
    <P>PostgreSQL is an enhancement of the POSTGRES database management system, a next-generation DBMS research prototype. While PostgreSQL retains the powerful data model and rich data types of POSTGRES, it replaces the PostQuel query language with an extended subset of SQL. PostgreSQL is free and the complete source is available.</P>

    <P>PostgreSQL development is performed by a team of Internet developers who all subscribe to the PostgreSQL development mailing list. The current coordinator is Marc G. Fournier (<A href="mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See below on how to join). This team is now responsible for all development of PostgreSQL.</P>

    <P>The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many others have contributed to the porting, testing, debugging, and enhancement of the code. The original Postgres code, from which PostgreSQL is derived, was the effort of many graduate students, undergraduate students, and staff programmers working under the direction of Professor Michael Stonebraker at the University of California, Berkeley.</P>

    <P>The original name of the software at Berkeley was Postgres. When SQL functionality was added in 1995, its name was changed to Postgres95. The name was changed at the end of 1996 to PostgreSQL.</P>
B
Update FAQ.  
Bruce Momjian 已提交
122 123 124 125 126 127 128 129 130 

    <P>It is pronounced <I>Post-Gres-Q-L.</I></P>

    <H4><A name="1.2">1.2</A>) What's the copyright on PostgreSQL?</H4>

    <P>PostgreSQL is subject to the following COPYRIGHT:</P>

    <P>PostgreSQL Data Base Management System</P>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
131 
    <P>Portions copyright (c) 1996-2000, PostgreSQL, Inc Portions Copyright (c) 1994-6 Regents of the University of California</P>
B
Update FAQ.  
Bruce Momjian 已提交
132
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
133 
    <P>Permission to use, copy, modify, and distribute this software and its documentation for any purpose, without fee, and without a written agreement is hereby granted, provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies.</P>
B
Update FAQ.  
Bruce Momjian 已提交
134
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
135 
    <P>IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.</P>
B
Update FAQ.  
Bruce Momjian 已提交
136
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
137 
    <P>THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.</P>
B
Update FAQ.  
Bruce Momjian 已提交
138
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
139 
    <H4><A name="1.3">1.3</A>) What Unix platforms does PostgreSQL run on?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
140
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
141 
    <P>In general, a modern Unix-compatible platform should be able to run PostgreSQL. The platforms that had received explicit testing at the time of release are listed in the installation instructions.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
142
B
Update FAQ.  
Bruce Momjian 已提交
143 
    <H4><A name="1.4">1.4</A>) What non-unix ports are available?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
144
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
145 
    <P>It is possible to compile the <I>libpq</I> C library, psql, and other interfaces and binaries to run on MS Windows platforms. In this case, the client is running on MS Windows, and communicates via TCP/IP to a server running on one of our supported Unix platforms. A file <I>win31.mak</I> is included in the distribution for making a Win32 <I>libpq</I> library and psql.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
146
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
147 
    <P>The database server can run on Windows NT and later using Cygwin, the Cygnus Unix/NT porting library. See <I>pgsql/doc/FAQ_MSWIN</I> in the distribution. The database server does not run on MS Windows 9X because Cygwin does not support the required features on those platforms. We have no plans to do a native port to any Microsoft platform.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
148
B
Update FAQ.  
Bruce Momjian 已提交
149 
    <H4><A name="1.5">1.5</A>) Where can I get PostgreSQL?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
150
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
151 
    <P>The primary anonymous ftp site for PostgreSQL is <A href="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A>. For mirror sites, see our main Web site.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
152
B
Update FAQ.  
Bruce Momjian 已提交
153 
    <H4><A name="1.6">1.6</A>) Where can I get support?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
154
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
155 
    <P>There is no support for PostgreSQL from the University of California, Berkeley. It is maintained through volunteer effort.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
156
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
157 
    <P>The main mailing list is: <A href="mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>. It is available for discussion of matters pertaining to PostgreSQL. To subscribe, send mail with the following lines in the body (not the subject line)</P>
B
Update FAQ.  
Bruce Momjian 已提交
158 159 160 161 
<PRE>
    subscribe
    end
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
162
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
163 
    <P>to <A href="mailto:pgsql-general-request@PostgreSQL.org">pgsql-general-request@PostgreSQL.org</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
164
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
165 
    <P>There is also a digest list available. To subscribe to this list, send email to: <A href="mailto:pgsql-general-digest-request@PostgreSQL.org">pgsql-general-digest-request@PostgreSQL.org</A> with a body of:</P>
B
Update FAQ.  
Bruce Momjian 已提交
166 167 168 169 
<PRE>
    subscribe
    end
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
170 
    Digests are sent out to members of this list whenever the main list has received around 30k of messages.
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
171
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
172 
    <P>The bugs mailing list is available. To subscribe to this list, send email to <A href="mailto:pgsql-bugs-request@PostgreSQL.org">pgsql-bugs-request@PostgreSQL.org</A> with a body of:</P>
B
Update FAQ.  
Bruce Momjian 已提交
173 174 175 176 
<PRE>
    subscribe
    end
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
177 
    There is also a developers discussion mailing list available. To subscribe to this list, send email to <A href="mailto:pgsql-hackers-request@PostgreSQL.org">pgsql-hackers-request@PostgreSQL.org</A> with a body of:
B
Update FAQ.  
Bruce Momjian 已提交
178 179 180 181 
<PRE>
    subscribe
    end
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
182
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
183 
    <P>Additional mailing lists and information about PostgreSQL can be found via the PostgreSQL WWW home page at:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
184
B
Update FAQ.  
Bruce Momjian 已提交
185 186 187 
    <BLOCKQUOTE>
      <A href="http://www.PostgreSQL.org">http://www.PostgreSQL.org</A>
    </BLOCKQUOTE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
188
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
189 
    <P>There is also an IRC channel on EFNet, channel <I>#PostgreSQL.</I> I use the unix command <CODE>irc -c '#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
190
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
191 
    <P>A list of commercial PostgreSQL support is available at <A href="http://www.postgresql.org/users-lounge/commercial-support.html">http://www.postgresql.org/users-lounge/commercial-support.html</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
192
B
Update FAQ.  
Bruce Momjian 已提交
193 
    <H4><A name="1.7">1.7</A>) What is the latest release?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
194
B
Update FAQ.  
Bruce Momjian 已提交
195 
    <P>The latest release of PostgreSQL is version 7.0.3.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
196
B
Update FAQ.  
Bruce Momjian 已提交
197 
    <P>We plan to have major releases every four months.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
198
B
Update FAQ.  
Bruce Momjian 已提交
199 
    <H4><A name="1.8">1.8</A>) What documentation is available?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
200
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
201 
    <P>Several manuals, manual pages, and some small test examples are included in the distribution. See the <I>/doc</I> directory. You can also browse the manual online at <A href="http://www.PostgreSQL.org/docs/postgres">http://www.PostgreSQL.org/docs/postgres</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
202
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
203 
    <P>There is a PostgreSQL book available at <A href="http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
204
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
205 
    <P><I>psql</I> has some nice \d commands to show information about types, operators, functions, aggregates, etc.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
206
B
Update FAQ.  
Bruce Momjian 已提交
207 208 
    <P>Our Web site contains even more documentation.</P>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
209 
    <H4><A name="1.9">1.9</A>) How do I find out about known bugs or missing features?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
210
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
211 
    <P>PostgreSQL supports an extended subset of SQL-92. See our <A href="http://www.PostgreSQL.org/docs/todo.html">TODO</A> list for known bugs, missing features, and future plans.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
212
B
Update FAQ.  
Bruce Momjian 已提交
213 214 
    <H4><A name="1.10">1.10</A>) How can I learn SQL?</H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
215 
    <P>The PostgreSQL book at <A href="http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A> teaches SQL. There is a nice tutorial at <A href="http://w3.one.net/~jhoffman/sqltut.htm">http://w3.one.net/~jhoffman/sqltut.htm</A> and at <A href="http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM">http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.</A></P>
B
Update FAQ.  
Bruce Momjian 已提交
216
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
217 
    <P>Another one is "Teach Yourself SQL in 21 Days, Second Edition" at <A href="http://members.tripod.com/er4ebus/sql/index.htm">http://members.tripod.com/er4ebus/sql/index.htm</A></P>
B
Update FAQ.  
Bruce Momjian 已提交
218
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
219 
    <P>Many of our users like <I>The Practical SQL Handbook</I>, Bowman, Judith S., et al., Addison-Wesley. Others like <I>The Complete Reference SQL</I>, Groff et al., McGraw-Hill.</P>
B
Update FAQ.  
Bruce Momjian 已提交
220 221 222 

    <H4><A name="1.11">1.11</A>) Is PostgreSQL Y2K compliant?</H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
223 
    <P>Yes, we easily handle dates past the year 2000AD, and before 2000BC.</P>
B
Update FAQ.  
Bruce Momjian 已提交
224
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
225 
    <H4><A name="1.12">1.12</A>) How do I join the development team?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
226
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
227 
    <P>First, download the latest source and read the PostgreSQL Developers documentation on our Web site, or in the distribution. Second, subscribe to the <I>pgsql-hackers</I> and <I>pgsql-patches</I> mailing lists. Third, submit high-quality patches to pgsql-patches.</P>
B
Update FAQ.  
Bruce Momjian 已提交
228
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
229 
    <P>There are about a dozen people who have commit privileges to the PostgreSQL CVS archive. They each have submitted so many high-quality patches that it was impossible for the existing committers to keep up, and we had confidence that patches they committed were of high quality.</P>
B
Update FAQ.  
Bruce Momjian 已提交
230 231 232 

    <H4><A name="1.13">1.13</A>) How do I submit a bug report?</H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
233 
    <P>Fill out the "bug-template" file and send it to: <A href="mailto:pgsql-bugs@PostgreSQL.org">pgsql-bugs@PostgreSQL.org</A></P>
B
Update FAQ.  
Bruce Momjian 已提交
234
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
235 
    <P>Also check out our ftp site <A href="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to see if there is a more recent PostgreSQL version or patches.</P>
B
Update FAQ.  
Bruce Momjian 已提交
236
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
237 
    <H4><A name="1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
238
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
239 
    <P>There are several ways of measuring software: features, performance, reliability, support, and price.</P>
B
Update FAQ.  
Bruce Momjian 已提交
240 241 242 243 

    <DL>
      <DT><B>Features</B></DT>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
244 
      <DD>PostgreSQL has most features present in large commercial DBMS's, like transactions, subselects, triggers, views, foreign key referential integrity, and sophisticated locking. We have some features they don't have, like user-defined types, inheritance, rules, and multi-version concurrency control to reduce lock contention. We don't have outer joins, but are working on them.<BR>
B
Update FAQ.  
Bruce Momjian 已提交
245 246 247 248 249 
      <BR>
      </DD>

      <DT><B>Performance</B></DT>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
250 
      <DD>PostgreSQL runs in two modes. Normal <I>fsync</I> mode flushes every completed transaction to disk, guaranteeing that if the OS crashes or loses power in the next few seconds, all your data is safely stored on disk. In this mode, we are slower than most commercial databases, partly because few of them do such conservative flushing to disk in their default modes. In <I>no-fsync</I> mode, we are usually faster than commercial databases, though in this mode, an OS crash could cause data corruption. We are working to provide an intermediate mode that suffers less performance overhead than full fsync mode, and will allow data integrity within 30 seconds of an OS crash.<BR>
B
Update FAQ.  
Bruce Momjian 已提交
251 
      <BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
252 
       In comparison to MySQL or leaner database systems, we are slower on inserts/updates because we have transaction overhead. Of course, MySQL doesn't have any of the features mentioned in the <I>Features</I> section above. We are built for flexibility and features, though we continue to improve performance through profiling and source code analysis. There is an interesting Web page comparing PostgreSQL to MySQL at <A href="http://openacs.org/why-not-mysql.html">http://openacs.org/why-not-mysql.html</A><BR>
B
Update FAQ.  
Bruce Momjian 已提交
253 
      <BR>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
254 
       We handle each user connection by creating a Unix process. Backend processes share data buffers and locking information. With multiple CPU's, multiple backends can easily run on different CPU's.<BR>
B
Update FAQ.  
Bruce Momjian 已提交
255 256 257 258 259 
      <BR>
      </DD>

      <DT><B>Reliability</B></DT>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
260 
      <DD>We realize that a DBMS must be reliable, or it is worthless. We strive to release well-tested, stable code that has a minimum of bugs. Each release has at least one month of beta testing, and our release history shows that we can provide stable, solid releases that are ready for production use. We believe we compare favorably to other database software in this area.<BR>
B
Update FAQ.  
Bruce Momjian 已提交
261 262 263 264 265 
      <BR>
      </DD>

      <DT><B>Support</B></DT>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
266 
      <DD>Our mailing list provides a large group of developers and users to help resolve any problems encountered. While we can not guarantee a fix, commercial DBMS's don't always supply a fix either. Direct access to developers, the user community, manuals, and the source code often make PostgreSQL support superior to other DBMS's. There is commercial per-incident support available for those who need it. (See support FAQ item.)<BR>
B
Update FAQ.  
Bruce Momjian 已提交
267 268 269 270 271 
      <BR>
      </DD>

      <DT><B>Price</B></DT>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
272 
      <DD>We are free for all use, both commercial and non-commercial. You can add our code to your product with no limitations, except those outlined in our BSD-style license stated above.<BR>
B
Update FAQ.  
Bruce Momjian 已提交
273 274 275 276 
      <BR>
      </DD>
    </DL>
    <HR>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
277
B
Update FAQ.  
Bruce Momjian 已提交
278 279 280 
    <CENTER>
      <H2>User Client Questions</H2>
    </CENTER>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
281
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
282 
    <H4><A name="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
283
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
284 
    <P>There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
285
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
286 
    <P>PsqlODBC is included in the distribution. More information about it can be gotten from <A href="ftp://ftp.PostgreSQL.org/pub/odbc/">ftp://ftp.PostgreSQL.org/pub/odbc/</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
287
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
288 
    <P>OpenLink ODBC can be gotten from <A href="http://www.openlinksw.com/">http://www.openlinksw.com</A>. It works with their standard ODBC client software so you'll have PostgreSQL ODBC available on every client platform they support (Win, Mac, Unix, VMS).</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
289
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
290 
    <P>They will probably be selling this product to people who need commercial-quality support, but a freeware version will always be available. Questions to <A href="mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
291
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
292 
    <P>See also the <A href="http://www.PostgreSQL.org/docs/programmer/odbc.htm">ODBC chapter of the Programmer's Guide</A>.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
293
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
294 
    <H4><A name="2.2">2.2</A>) What tools are available for hooking PostgreSQL to Web pages?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
295
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
296 
    <P>A nice introduction to Database-backed Web pages can be seen at: <A href="http://www.webtools.com">http://www.webtools.com</A></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
297
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
298 
    <P>There is also one at <A href="http://www.phone.net/home/mwm/hotlist/">http://www.phone.net/home/mwm/hotlist/.</A></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
299
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
300 
    <P>For Web integration, PHP is an excellent interface. It is at <A href="http://www.php.net">http://www.php.net</A></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
301
B
Update FAQ.  
Bruce Momjian 已提交
302 
    <P>For complex cases, many use the Perl interface and CGI.pm.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
303
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
304 
    <P>A WWW gateway based on WDB using Perl can be downloaded from <A href="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb-p95</A></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
305
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
306 
    <H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
307
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
308 
    <P>We have a nice graphical user interface called <I>pgaccess,</I> which is shipped as part of the distribution. <I>Pgaccess</I> also has a report generator. The Web page is <A href="http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
309
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
310 
    <P>We also include <I>ecpg,</I> which is an embedded SQL query language interface for C.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
311
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
312 
    <H4><A name="2.4">2.4</A>) What languages are available to communicate with PostgreSQL?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
313
B
Update FAQ.  
Bruce Momjian 已提交
314 
    <P>We have:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
315
B
Update FAQ.  
Bruce Momjian 已提交
316 317 
    <UL>
      <LI>C (libpq)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
318
B
Update FAQ.  
Bruce Momjian 已提交
319 
      <LI>C++ (libpq++)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
320
B
Update FAQ.  
Bruce Momjian 已提交
321 
      <LI>Embedded C (ecpg)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
322
B
Update FAQ.  
Bruce Momjian 已提交
323 
      <LI>Java (jdbc)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
324
B
Update FAQ.  
Bruce Momjian 已提交
325 
      <LI>Perl (perl5)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
326
B
Update FAQ.  
Bruce Momjian 已提交
327 
      <LI>ODBC (odbc)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
328
B
Update FAQ.  
Bruce Momjian 已提交
329 
      <LI>Python (PyGreSQL)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
330
B
Update FAQ.  
Bruce Momjian 已提交
331 
      <LI>TCL (libpgtcl)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
332
B
Update FAQ.  
Bruce Momjian 已提交
333 
      <LI>C Easy API (libpgeasy)</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
334
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
335 
      <LI>Embedded HTML (<A href="http://www.php.net">PHP from http://www.php.net</A>)</LI>
B
Update FAQ.  
Bruce Momjian 已提交
336 337 
    </UL>
    <HR>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
338
B
Update FAQ.  
Bruce Momjian 已提交
339 340 341 
    <CENTER>
      <H2>Administrative Questions</H2>
    </CENTER>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
342
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
343 
    <H4><A name="3.1">3.1</A>) How do I install PostgreSQL somewhere other than <I>/usr/local/pgsql?</I></H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
344
B
Update FAQ.  
Bruce Momjian 已提交
345 
    <P>Specify the <I>--prefix</I> option when running <I>configure.</I></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
346
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 
    <H4><A name="3.2">3.2</A>) When I start the <I>postmaster</I>, I get a <I>Bad System Call</I> or core dumped message. Why?</H4>

    <P>It could be a variety of problems, but first check to see that you have System V extensions installed in your kernel. PostgreSQL requires kernel support for shared memory and semaphores.</P>

    <H4><A name="3.3">3.3</A>) When I try to start the <I>postmaster,</I> I get <I>IpcMemoryCreate</I> errors. Why?</H4>

    <P>You either do not have shared memory configured properly in your kernel or you need to enlarge the shared memory available in the kernel. The exact amount you need depends on your architecture and how many buffers and backend processes you configure for the <I>postmaster.</I> For most systems, with default numbers of buffers and processes, you need a minimum of ~1MB.</P>

    <H4><A name="3.4">3.4</A>) When I try to start the <I>postmaster,</I> I get <I>IpcSemaphoreCreate</I> errors. Why?</H4>

    <P>If the error message is <I>IpcSemaphoreCreate: semget failed (No space left on device)</I> then your kernel is not configured with enough semaphores. Postgres needs one semaphore per potential backend process. A temporary solution is to start the <I>postmaster</I> with a smaller limit on the number of backend processes. Use <I>-N</I> with a parameter less than the default of 32. A more permanent solution is to increase your kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.</P>

    <P>If the error message is something else, you might not have semaphore support configured in your kernel at all.</P>

    <H4><A name="3.5">3.5</A>) How do I prevent other hosts from accessing my PostgreSQL database?</H4>

    <P>By default, PostgreSQL only allows connections from the local machine using Unix domain sockets. Other machines will not be able to connect unless you add the <I>-i</I> flag to the <I>postmaster,</I> <B>and</B> enable host-based authentication by modifying the file <I>$PGDATA/pg_hba.conf</I> accordingly. This will allow TCP/IP connections.</P>

    <H4><A name="3.6">3.6</A>) Why can't I connect to my database from another machine?</H4>

    <P>The default configuration allows only unix domain socket connections from the local machine. To enable TCP/IP connections, make sure the <I>postmaster</I> has been started with the <I>-i</I> option, and add an appropriate host entry to the file <I>pgsql/data/pg_hba.conf</I>.</P>

    <H4><A name="3.7">3.7</A>) All my servers crash under concurrent table access. Why?</H4>

    <P>This problem can be caused by a kernel that is not configured to support semaphores.</P>

    <H4><A name="3.8">3.8</A>) How do I tune the database engine for better performance?</H4>

    <P>Certainly, indices can speed up queries. The <SMALL>EXPLAIN</SMALL> command allows you to see how PostgreSQL is interpreting your query, and which indices are being used.</P>

    <P>If you are doing a lot of <SMALL>INSERTs</SMALL>, consider doing them in a large batch using the <SMALL>COPY</SMALL> command. This is much faster than individual <SMALL>INSERTS.</SMALL> Second, statements not in a <SMALL>BEGIN WORK/COMMIT</SMALL> transaction block are considered to be in their own transaction. Consider performing several statements in a single transaction block. This reduces the transaction overhead. Also consider dropping and recreating indices when making large data changes.</P>

    <P>There are several tuning options. You can disable <I>fsync()</I> by starting the <I>postmaster</I> with a <I>-o -F</I> option. This will prevent <I>fsync()'s</I> from flushing to disk after every transaction.</P>

    <P>You can also use the <I>postmaster</I> <I>-B</I> option to increase the number of shared memory buffers used by the backend processes. If you make this parameter too high, the <I>postmaster</I> may not start because you've exceeded your kernel's limit on shared memory space. Each buffer is 8K and the default is 64 buffers.</P>

    <P>You can also use the backend <I>-S</I> option to increase the maximum amount of memory used by the backend process for temporary sorts. The <I>-S</I> value is measured in kilobytes, and the default is 512 (ie, 512K).</P>

    <P>You can also use the <SMALL>CLUSTER</SMALL> command to group data in tables to match an index. See the <SMALL>CLUSTER</SMALL> manual page for more details.</P>

    <H4><A name="3.9">3.9</A>) What debugging features are available?</H4>

    <P>PostgreSQL has several features that report status information that can be valuable for debugging purposes.</P>

    <P>First, by running <I>configure</I> with the --enable-cassert option, many <I>assert()'s</I> monitor the progress of the backend and halt the program when something unexpected occurs.</P>

    <P>Both <I>postmaster</I> and <I>postgres</I> have several debug options available. First, whenever you start the <I>postmaster,</I> make sure you send the standard output and error to a log file, like:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
394 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
395 396 397 
    cd /usr/local/pgsql
    ./bin/postmaster &gt;server.log 2&gt;&amp;1 &amp;
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
398
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 
    <P>This will put a server.log file in the top-level PostgreSQL directory. This file contains useful information about problems or errors encountered by the server. <I>Postmaster</I> has a <I>-d</I> option that allows even more detailed information to be reported. The <I>-d</I> option takes a number that specifies the debug level. Be warned that high debug level values generate large log files.</P>

    <P>If the <I>postmaster</I> is not running, you can actually run the <I>postgres</I> backend from the command line, and type your SQL statement directly. This is recommended <B>only</B> for debugging purposes. Note that a newline terminates the query, not a semicolon. If you have compiled with debugging symbols, you can use a debugger to see what is happening. Because the backend was not started from the <I>postmaster,</I> it is not running in an identical environment and locking/backend interaction problems may not be duplicated.</P>

    <P>If the <I>postmaster</I> is running, start <I>psql</I> in one window, then find the <SMALL>PID</SMALL> of the <I>postgres</I> process used by <I>psql.</I> Use a debugger to attach to the <I>postgres</I> <SMALL>PID.</SMALL> You can set breakpoints in the debugger and issue queries from <I>psql.</I> If you are debugging <I>postgres</I> startup, you can set PGOPTIONS="-W n", then start <I>psql.</I> This will cause startup to delay for <I>n</I> seconds so you can attach with the debugger and trace through the startup sequence.</P>

    <P>The <I>postgres</I> program has <I>-s, -A,</I> and <I>-t</I> options that can be very useful for debugging and performance measurements.</P>

    <P>You can also compile with profiling to see what functions are taking execution time. The backend profile files will be deposited in the <I>pgsql/data/base/dbname</I> directory. The client profile file will be put in the client's current directory.</P>

    <H4><A name="3.10">3.10</A>) I get 'Sorry, too many clients' when trying to connect. Why?</H4>

    <P>You need to increase the <I>postmaster's</I> limit on how many concurrent backend processes it can start.</P>

    <P>In PostgreSQL 6.5 and up, the default limit is 32 processes. You can increase it by restarting the <I>postmaster</I> with a suitable <I>-N</I> value. With the default configuration you can set <I>-N</I> as large as 1024. If you need more, increase <SMALL>MAXBACKENDS</SMALL> in <I>include/config.h</I> and rebuild. You can set the default value of <I>-N</I> at configuration time, if you like, using <I>configure's</I> <I>--with-maxbackends</I> switch.</P>

    <P>Note that if you make <I>-N</I> larger than 32, you must also increase <I>-B</I> beyond its default of 64; <I>-B</I> must be at least twice <I>-N,</I> and probably should be more than that for best performance. For large numbers of backend processes, you are also likely to find that you need to increase various Unix kernel configuration parameters. Things to check include the maximum size of shared memory blocks, <SMALL>SHMMAX;</SMALL> the maximum number of semaphores, <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI;</SMALL> the maximum number of processes, <SMALL>NPROC;</SMALL> the maximum number of processes per user, <SMALL>MAXUPRC;</SMALL> and the maximum number of open files, <SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that PostgreSQL has a limit on the number of allowed backend processes is so your system won't run out of resources.</P>

    <P>In PostgreSQL versions prior to 6.5, the maximum number of backends was 64, and changing it required a rebuild after altering the MaxBackendId constant in <I>include/storage/sinvaladt.h.</I></P>

    <H4><A name="3.11">3.11</A>) What are the <I>pg_sorttempNNN.NN</I> files in my database directory?</H4>

    <P>They are temporary files generated by the query executor. For example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and the sort requires more space than the backend's <I>-S</I> parameter allows, then temporary files are created to hold the extra data.</P>

    <P>The temporary files should be deleted automatically, but might not if a backend crashes during a sort. If you have no backends running at the time, it is safe to delete the pg_tempNNN.NN files.</P>
B
Update FAQ.  
Bruce Momjian 已提交
424 425 426 427 428 429 
    <HR>

    <CENTER>
      <H2>Operational Questions</H2>
    </CENTER>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
430 
    <H4><A name="4.1">4.1</A>) Why is system confused about commas, decimal points, and date formats.</H4>
B
Update FAQ.  
Bruce Momjian 已提交
431
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
432 
    <P>Check your locale configuration. PostgreSQL uses the locale setting of the user that ran the <I>postmaster</I> process. There are postgres and psql SET commands to control the date format. Set those accordingly for your operating environment.</P>
B
Update FAQ.  
Bruce Momjian 已提交
433
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
434 
    <H4><A name="4.2">4.2</A>) What is the exact difference between binary cursors and normal cursors?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
435
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
436 
    <P>See the <SMALL>DECLARE</SMALL> manual page for a description.</P>
B
Update FAQ.  
Bruce Momjian 已提交
437
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
438 
    <H4><A name="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
439
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
440 
    <P>See the <SMALL>FETCH</SMALL> manual page, or use SELECT ... LIMIT....</P>
B
Update FAQ.  
Bruce Momjian 已提交
441
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
442 
    <P>The entire query may have to be evaluated, even if you only want the first few rows. Consider a query that has an <SMALL>ORDER BY.</SMALL> If there is an index that matches the <SMALL>ORDER BY</SMALL>, PostgreSQL may be able to evaluate only the first few records requested, or the entire query may have to be evaluated until the desired rows have been generated.</P>
B
Update FAQ.  
Bruce Momjian 已提交
443
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
444 
    <H4><A name="4.4">4.4</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR>
B
Update FAQ.  
Bruce Momjian 已提交
445 446 
    </H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
447 
    <P>You can read the source code for <I>psql</I> in file <I>pgsql/src/bin/psql/describe.c.</I> It contains SQL commands that generate the output for psql's backslash commands. You can also start <I>psql</I> with the <I>-E</I> option so it will print out the queries it uses to execute the commands you give.</P>
B
Update FAQ.  
Bruce Momjian 已提交
448
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
449 
    <H4><A name="4.5">4.5</A>) How do you remove a column from a table?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
450
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
451 
    <P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do this:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
452 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
453 454 455 456 457 458 
    SELECT ...  -- select all columns but the one you want to remove
    INTO TABLE new_table
    FROM old_table;
    DROP TABLE old_table;
    ALTER TABLE new_table RENAME TO old_table;
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
459
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
460 
    <H4><A name="4.6">4.6</A>) What is the maximum size for a row, table, database?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
461
B
Update FAQ.  
Bruce Momjian 已提交
462 
    <P>These are the limits:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
463 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
464 
Maximum size for a database?             unlimited (60GB databases exist)
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
465 
Maximum size for a table?                unlimited on all operating systems
B
Update FAQ.  
Bruce Momjian 已提交
466 467 
Maximum size for a row?                  unlimited in 7.1 and later
Maximum number of rows in a table?       unlimited
B
Update FAQ.  
Bruce Momjian 已提交
468 
Maximum number of columns in a table?    unlimited
B
Update FAQ.  
Bruce Momjian 已提交
469 
Maximum number of indexes on a table?    unlimited
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
470 
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
471 
    Of course, these are not actually unlimited, but limited to available disk space.
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
472
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
473 
    <H4><A name="4.7">4.7</A>) How much database disk space is required to store data from a typical text file?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
474 
    </H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
475
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
476 
    <P>A PostgreSQL database may need six-and-a-half times the disk space required to store the data in a flat file.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
477
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
478 
    <P>Consider a file of 300,000 lines with two integers on each line. The flat file is 2.4MB. The size of the PostgreSQL database file containing this data can be estimated at 14MB:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 
<PRE>
    36 bytes: each row header (approximate)
   + 8 bytes: two int fields @ 4 bytes each
   + 4 bytes: pointer on page to tuple
   ----------------------------------------
    48 bytes per row

   The data page size in PostgreSQL is 8192 bytes (8 KB), so:

   8192 bytes per page
   -------------------   =  171 rows per database page (rounded up)
     48 bytes per row

   300000 data rows
   --------------------  =  1755 database pages
      171 rows per page

1755 database pages * 8192 bytes per page  =  14,376,960 bytes (14MB)
B
Update FAQ.  
Bruce Momjian 已提交
497 
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
498
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
499 
    <P>Indexes do not require as much overhead, but do contain the data that is being indexed, so they can be large also.</P>
B
Update FAQ.  
Bruce Momjian 已提交
500
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
501 
    <H4><A name="4.8">4.8</A>) How do I find out what indices or operations are defined in the database?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
502
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
503 
    <P><I>psql</I> has a variety of backslash commands to show such information. Use \? to see them.</P>
B
Update FAQ.  
Bruce Momjian 已提交
504
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
505 
    <P>Also try the file <I>pgsql/src/tutorial/syscat.source.</I> It illustrates many of the <SMALL>SELECT</SMALL>s needed to get information from the database system tables.</P>
B
Update FAQ.  
Bruce Momjian 已提交
506
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
507 
    <H4><A name="4.9">4.9</A>) My queries are slow or don't make use of the indexes. Why?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
508
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
509 
    <P>PostgreSQL does not automatically maintain statistics. V<SMALL>ACUUM</SMALL> must be run to update the statistics. After statistics are updated, the optimizer knows how many rows in the table, and can better decide if it should use indices. Note that the optimizer does not use indices in cases when the table is small because a sequential scan would be faster.</P>
B
Update FAQ.  
Bruce Momjian 已提交
510
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
511 
    <P>For column-specific optimization statistics, use <SMALL>VACUUM ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for complex multijoin queries, so the optimizer can estimate the number of rows returned from each table, and choose the proper join order. The backend does not keep track of column statistics on its own, so <SMALL>VACUUM ANALYZE</SMALL> must be run to collect them periodically.</P>
B
Update FAQ.  
Bruce Momjian 已提交
512
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
513 
    <P>Indexes are usually not used for <SMALL>ORDER BY</SMALL> operations: a sequential scan followed by an explicit sort is faster than an indexscan of all tuples of a large table, because it takes fewer disk accesses.</P>
B
Update FAQ.  
Bruce Momjian 已提交
514
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
515 
    <P>When using wild-card operators such as <SMALL>LIKE</SMALL> or <I>~,</I> indices can only be used if the beginning of the search is anchored to the start of the string. So, to use indices, <SMALL>LIKE</SMALL> searches should not begin with <I>%,</I> and <I>~</I>(regular expression searches) should start with <I>^.</I></P>
B
Update FAQ.  
Bruce Momjian 已提交
516
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
517 
    <H4><A name="4.10">4.10</A>) How do I see how the query optimizer is evaluating my query?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
518 519 520 521 522 

    <P>See the <SMALL>EXPLAIN</SMALL> manual page.</P>

    <H4><A name="4.11">4.11</A>) What is an R-tree index?</H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
523 
    <P>An R-tree index is used for indexing spatial data. A hash index can't handle range searches. A B-tree index only handles range searches in a single dimension. R-tree's can handle multi-dimensional data. For example, if an R-tree index can be built on an attribute of type <I>point,</I> the system can more efficiently answer queries such as "select all points within a bounding rectangle."</P>
B
Update FAQ.  
Bruce Momjian 已提交
524
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
525 
    <P>The canonical paper that describes the original R-tree design is:</P>
B
Update FAQ.  
Bruce Momjian 已提交
526
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
527 
    <P>Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.</P>
B
Update FAQ.  
Bruce Momjian 已提交
528
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
529 
    <P>You can also find this paper in Stonebraker's "Readings in Database Systems".</P>
B
Update FAQ.  
Bruce Momjian 已提交
530
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
531 
    <P>Built-in R-trees can handle polygons and boxes. In theory, R-trees can be extended to handle higher number of dimensions. In practice, extending R-trees requires a bit of work and we don't currently have any documentation on how to do it.</P>
B
Update FAQ.  
Bruce Momjian 已提交
532
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
533 
    <H4><A name="4.12">4.12</A>) What is Genetic Query Optimization?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
534
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
535 
    <P>The GEQO module speeds query optimization when joining many tables by means of a Genetic Algorithm (GA). It allows the handling of large join queries through nonexhaustive search.</P>
B
Update FAQ.  
Bruce Momjian 已提交
536
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
537 
    <H4><A name="4.13">4.13</A>) How do I do regular expression searches and case-insensitive regular expression searches?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
538
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
539 
    <P>The <I>~</I> operator does regular expression matching, and <I>~*</I> does case-insensitive regular expression matching. There is no case-insensitive variant of the LIKE operator, but you can get the effect of case-insensitive <SMALL>LIKE</SMALL> with this:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
540 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
541 
    WHERE lower(textfield) LIKE lower(pattern)
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
542 543 
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
544 
    <H4><A name="4.14">4.14</A>) In a query, how do I detect if a field is NULL?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
545
B
Update FAQ.  
Bruce Momjian 已提交
546 
    <P>You test the column with IS NULL and IS NOT NULL.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
547
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
548 
    <H4><A name="4.15">4.15</A>) What is the difference between the various character types?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
549 550 551 552 553 554 
<PRE>
Type            Internal Name   Notes
--------------------------------------------------
"char"          char            1 character
CHAR(#)         bpchar          blank padded to the specified fixed length
VARCHAR(#)      varchar         size specifies maximum length, no padding
T
Remove obsolete claim that char(n) is more efficient than other text types.  
Tom Lane 已提交
555 556 
TEXT            text            no specific upper limit on length
BYTEA           bytea           variable-length byte array (null-safe)
B
Update FAQ.  
Bruce Momjian 已提交
557 
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
558
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
559 
    <P>You will see the internal name when examining system catalogs and in some error messages.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
560
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
561 
    <P>The last four types above are "varlena" types (i.e., the first four bytes on disk are the length, followed by the data). Thus the actual space used is slightly greater than the declared size. However, these data types are also subject to compression or being stored out-of-line by TOAST, so the space on disk might also be less than expected.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
562
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
563 
    <H4><A name="4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
564
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
565 
    <P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It auto-creates a sequence and index on the column. For example, this:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
566 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
567 568 569 570 
    CREATE TABLE person ( 
        id   SERIAL, 
        name TEXT 
    );
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
571 
</PRE>
B
Update FAQ.  
Bruce Momjian 已提交
572 
    is automatically translated into this:
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
573 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
574 575 576 577 578 579 
    CREATE SEQUENCE person_id_seq;
    CREATE TABLE person ( 
        id   INT4 NOT NULL DEFAULT nextval('person_id_seq'),
        name TEXT 
    );
    CREATE UNIQUE INDEX person_id_key ON person ( id );
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
580 
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
581 582 583 584 585 586 587 
    See the <I>create_sequence</I> manual page for more information about sequences. You can also use each row's <I>OID</I> field as a unique value. However, if you need to dump and reload the database, you need to use <I>pg_dump's -o</I> option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the <SMALL>OID</SMALL>s. 

    <P><A href="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A></P>

    <H4><A name="4.16.2">4.16.2</A>) How do I get the value of a <SMALL>SERIAL</SMALL> insert?</H4>

    <P>One approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A href="#4.16.1">4.16.1</A>, that might look like this:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
588 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
589 590 
    $newSerialID = nextval('person_id_seq');
    INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
591 
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
592 593 594 
    You would then also have the new value stored in <CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign key to the <CODE>person</CODE> table). Note that the name of the automatically created SEQUENCE object will be named &lt;<I>table</I>&gt;_&lt;<I>serialcolumn</I>&gt;_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table and your SERIAL column, respectively. 

    <P>Alternatively, you could retrieve the assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
595 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
596 597 
    INSERT INTO person (name) VALUES ('Blaise Pascal');
    $newID = currval('person_id_seq');
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
598 
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
599 
    Finally, you could use the <A href="#4.17"><SMALL>OID</SMALL></A> returned from the INSERT statement to look up the default value, though this is probably the least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid value is made available via <I>$sth-&gt;{pg_oid_status} after $sth-&gt;execute().</I>
B
Update FAQ.  
Bruce Momjian 已提交
600
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
601 
    <H4><A name="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?</H4>
B
Update FAQ.  
Bruce Momjian 已提交
602 603 604 

    <P>No. This is handled by the backends.</P>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
605 606 607 608 609 610 611 
    <H4><A name="4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a <SMALL>TID</SMALL>?</H4>

    <P><SMALL>OID</SMALL>s are PostgreSQL's answer to unique row ids. Every row that is created in PostgreSQL gets a unique <SMALL>OID</SMALL>. All <SMALL>OID</SMALL>s generated during <I>initdb</I> are less than 16384 (from <I>backend/access/transam.h</I>). All user-created <SMALL>OID</SMALL>s are equal to or greater than this. By default, all these <SMALL>OID</SMALL>s are unique not only within a table or database, but unique within the entire PostgreSQL installation.</P>

    <P>PostgreSQL uses <SMALL>OID</SMALL>s in its internal system tables to link rows between tables. These <SMALL>OID</SMALL>s can be used to identify specific user rows and used in joins. It is recommended you use column type <SMALL>OID</SMALL> to store <SMALL>OID</SMALL> values. You can create an index on the <SMALL>OID</SMALL> field for faster access.</P>

    <P>O<SMALL>id</SMALL>s are assigned to all new rows from a central area that is used by all databases. If you want to change the <SMALL>OID</SMALL> to something else, or if you want to make a copy of the table, with the original <SMALL>OID</SMALL>'s, there is no reason you can't do it:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
612 613 
<PRE>
        CREATE TABLE new_table(old_oid oid, mycol int);
B
Update FAQ.  
Bruce Momjian 已提交
614 
        SELECT old_oid, mycol INTO new FROM old;
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
615 616 617 618 
        COPY new TO '/tmp/pgtable';
        DELETE FROM new;
        COPY new WITH OIDS FROM '/tmp/pgtable';
<!--
B
Update FAQ.  
Bruce Momjian 已提交
619 620 
    CREATE TABLE new_table (mycol int);
    INSERT INTO new_table (oid, mycol) SELECT oid, mycol FROM old_table;
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
621 
-->
B
Update FAQ.  
Bruce Momjian 已提交
622 
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
623
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
624 
    <P>O<SMALL>ID</SMALL>s are stored as 4-byte integers, and will overflow at 4 billion. No one has reported this ever happening, and we plan to have the limit removed before anyone does.</P>
B
Update FAQ.  
Bruce Momjian 已提交
625
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
626 
    <P>T<SMALL>ID</SMALL>s are used to identify specific physical rows with block and offset values. Tids change after rows are modified or reloaded. They are used by index entries to point to physical rows.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
627
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
628 
    <H4><A name="4.18">4.18</A>) What is the meaning of some of the terms used in PostgreSQL?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
629
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
630 
    <P>Some of the source code and older documentation use terms that have more common usage. Here are some:</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
631
B
Update FAQ.  
Bruce Momjian 已提交
632 633 
    <UL>
      <LI>table, relation, class</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
634
B
Update FAQ.  
Bruce Momjian 已提交
635 
      <LI>row, record, tuple</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
636
B
Update FAQ.  
Bruce Momjian 已提交
637 
      <LI>column, field, attribute</LI>
B
Update FAQ.  
Bruce Momjian 已提交
638
B
Update FAQ.  
Bruce Momjian 已提交
639 
      <LI>retrieve, select</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
640
B
Update FAQ.  
Bruce Momjian 已提交
641 
      <LI>replace, update</LI>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
642
B
Update FAQ.  
Bruce Momjian 已提交
643 644 645 646 647 648 649 650 651 
      <LI>append, insert</LI>

      <LI><SMALL>OID</SMALL>, serial value</LI>

      <LI>portal, cursor</LI>

      <LI>range variable, table name, table alias</LI>
    </UL>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
652 
    <P>A list of general database terms can be found at: <A href="http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
653
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
654 
    <H4><A name="4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc failure: memory exhausted?"</I><BR>
B
Update FAQ.  
Bruce Momjian 已提交
655 656 
    </H4>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
657 
    <P>It is possible you have run out of virtual memory on your system, or your kernel has a low limit for certain resources. Try this before starting the <I>postmaster:</I></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
658 
<PRE>
B
Update FAQ.  
Bruce Momjian 已提交
659 660 
    ulimit -d 65536
    limit datasize 64m
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
661 
</PRE>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
662 663 664 
    Depending on your shell, only one of these may succeed, but it will set your process data segment limit much higher and perhaps allow the query to complete. This command applies to the current process, and all subprocesses created after the command is run. If you are having a problem with the SQL client because the backend is returning too much data, try it before starting the client. 

    <H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version I am running?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
665 666 667 668 
    </H4>

    <P>From <I>psql,</I> type <CODE>select version();</CODE></P>
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
669 
    <H4><A name="4.21">4.21</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
670 
    </H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
671
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
672 
    <P>You need to put <CODE>BEGIN WORK</CODE> and <CODE>COMMIT</CODE> around any use of a large object handle, that is, surrounding <CODE>lo_open</CODE> ... <CODE>lo_close.</CODE></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
673
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
674 
    <P>Currently PostgreSQL enforces the rule by closing large object handles at transaction commit. So the first attempt to do anything with the handle will draw <I>invalid large obj descriptor.</I> So code that used to work (at least most of the time) will now generate that error message if you fail to use a transaction.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
675
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
676 
    <P>If you are using a client interface like ODBC you may need to set <CODE>auto-commit off.</CODE></P>
B
Update FAQ.  
Bruce Momjian 已提交
677
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
678 
    <H4><A name="4.22">4.22</A>) How do I create a column that will default to the current time?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
679 680 681 682 683 684 685 
    </H4>

    <P>Use <I>now()</I>:</P>
<PRE>
<CODE>CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
</CODE>
</PRE>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
686
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
687 
    <H4><A name="4.23">4.23</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
B
Update FAQ.  
Bruce Momjian 已提交
688 
    </H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
689
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
690 
    <P>Currently, we join subqueries to outer queries by sequentially scanning the result of the subquery for each row of the outer query. A workaround is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>:</P>
B
Update FAQ.  
Bruce Momjian 已提交
691 692 693 694 695 696 697 698 699 700 701 702 703 704 
<PRE>
<CODE>SELECT *
    FROM tab
    WHERE col1 IN (SELECT col2 FROM TAB2)
</CODE>
</PRE>
    to: 
<PRE>
<CODE>SELECT *
    FROM tab
    WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
</CODE>
</PRE>
    We hope to fix this limitation in a future release.
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
705
B
Update FAQ.  
Bruce Momjian 已提交
706 707 
    <H4><A name="4.24">4.24</A>) How do I do an <I>outer</I> join?<BR>
    </H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
708
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
709 
    <P>PostgreSQL 7.1 and later supports outer joins. In previous releases, outer joins can be simulated using <SMALL>UNION</SMALL> and <SMALL>NOT IN</SMALL>. For example, when joining <I>tab1</I> and <I>tab2,</I> the following query does an <I>outer</I> join of the two tables:</P>
B
Update FAQ.  
Bruce Momjian 已提交
710 711 712 713 714 715 716 717 718 719 720 
<PRE>
    SELECT tab1.col1, tab2.col2
    FROM tab1, tab2
    WHERE tab1.col1 = tab2.col1
    UNION ALL
    SELECT tab1.col1, NULL
    FROM tab1
    WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
    ORDER BY tab1.col1
</PRE>
    <HR>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
721
B
Update FAQ.  
Bruce Momjian 已提交
722 723 724 
    <CENTER>
      <H2>Extending PostgreSQL</H2>
    </CENTER>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
725
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
726 
    <H4><A name="5.1">5.1</A>) I wrote a user-defined function. When I run it in <I>psql,</I> why does it dump core?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
727
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
728 
    <P>The problem could be a number of things. Try testing your user-defined function in a stand-alone test program first.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
729
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
730 
    <H4><A name="5.2">5.2</A>) What does the message <I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
731
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
732 
    <P>You are <I>pfree'</I>ing something that was not <I>palloc'</I>ed. Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I></P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
733
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
734 
    <H4><A name="5.3">5.3</A>) How can I contribute some nifty new types and functions to PostgreSQL?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
735
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
736 
    <P>Send your extensions to the <I>pgsql-hackers</I> mailing list, and they will eventually end up in the <I>contrib/</I> subdirectory.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
737
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
738 
    <H4><A name="5.4">5.4</A>) How do I write a C function to return a tuple?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
739
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
740 
    <P>This requires wizardry so extreme that the authors have never tried it, though in principle it can be done.</P>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
741
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
742 
    <H4><A name="5.5">5.5</A>) I have changed a source file. Why does the recompile not see the change?</H4>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
743
B
Make Kevin Lo's MS FAQ the default.  
Bruce Momjian 已提交
744 
    <P>The <I>Makefiles</I> do not have the proper dependencies for include files. You have to do a <I>make clean</I> and then another <I>make</I>. If you are using GCC you can use the <I>--enable-depend</I> option of <I>configure</I> to have the compiler compute the dependencies automatically.</P>
B
Update FAQ.  
Bruce Momjian 已提交
745 
  </BODY>
B
Move FAQ source into main cvs tree.  
Bruce Momjian 已提交
746 747 
</HTML>