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865d26fd
编写于
2月 18, 2002
作者:
B
Bruce Momjian
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doc/FAQ
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865d26fd
Frequently Asked Questions (FAQ) for PostgreSQL
Last updated:
Thu Feb 14 12:14:47
EST 2002
Last updated:
Mon Feb 18 00:08:54
EST 2002
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
...
...
@@ -667,26 +667,26 @@
As an example, consider a file of 100,000 lines with an integer and
text description on each line. Suppose the text string avergages
twenty
characters in length. The flat file would be 2.8 MB. The siz
e
of the PostgreSQL database file containing this data can be estimated
as 6.6
MB:
twenty
bytes in length. The flat file would be 2.8 MB. The size of th
e
PostgreSQL database file containing this data can be estimated as 6.4
MB:
36 bytes: each row header (approximate)
2
6 bytes: two int fields @ 4 bytes each
2
4 bytes: one int field and one text filed
+ 4 bytes: pointer on page to tuple
----------------------------------------
6
6
bytes per row
6
4
bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 12
4
rows per database page (rounded down)
6
6
bytes per row
------------------- = 12
8
rows per database page (rounded down)
6
4
bytes per row
100000 data rows
-------------------- =
807
database pages (rounded up)
12
4
rows per page
-------------------- =
782
database pages (rounded up)
12
8
rows per page
807 database pages * 8192 bytes per page = 6,610,944 bytes (6.6
MB)
782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4
MB)
Indexes do not require as much overhead, but do contain the data that
is being indexed, so they can be large also.
...
...
doc/src/FAQ/FAQ.html
浏览文件 @
865d26fd
...
...
@@ -14,7 +14,7 @@
alink=
"#0000ff"
>
<H1>
Frequently Asked Questions (FAQ) for PostgreSQL
</H1>
<P>
Last updated:
Thu Feb 14 12:14:47
EST 2002
</P>
<P>
Last updated:
Mon Feb 18 00:08:54
EST 2002
</P>
<P>
Current maintainer: Bruce Momjian (
<A
href=
"mailto:pgman@candle.pha.pa.us"
>
pgman@candle.pha.pa.us
</A>
)
<BR>
...
...
@@ -855,27 +855,27 @@
<P>
As an example, consider a file of 100,000 lines with an integer
and text description on each line. Suppose the text string avergages
twenty
character
s in length. The flat file would be 2.8 MB. The size
twenty
byte
s in length. The flat file would be 2.8 MB. The size
of the PostgreSQL database file containing this data can be
estimated as 6.
6
MB:
</P>
estimated as 6.
4
MB:
</P>
<PRE>
36 bytes: each row header (approximate)
2
6 bytes: two int fields @ 4 bytes each
2
4 bytes: one int field and one text filed
+ 4 bytes: pointer on page to tuple
----------------------------------------
6
6
bytes per row
6
4
bytes per row
The data page size in PostgreSQL is 8192 bytes (8 KB), so:
8192 bytes per page
------------------- = 12
4
rows per database page (rounded down)
6
6
bytes per row
------------------- = 12
8
rows per database page (rounded down)
6
4
bytes per row
100000 data rows
-------------------- =
807
database pages (rounded up)
12
4
rows per page
-------------------- =
782
database pages (rounded up)
12
8
rows per page
807 database pages * 8192 bytes per page = 6,610,944 bytes (6.6
MB)
782 database pages * 8192 bytes per page = 6,406,144 bytes (6.4
MB)
</PRE>
<P>
Indexes do not require as much overhead, but do contain the data
...
...
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