bgwriter_lru_maxpages is exceeded leaves the loop variables in the
expected state.  In the original coding, we'd fail to advance
next_to_clean, causing that buffer to be probably-uselessly rechecked next
time, and also have an off-by-one idea of the number of buffers scanned.

buffers that cannot possibly need to be cleaned, and estimates how many
buffers it should try to clean based on moving averages of recent allocation
requests and density of reusable buffers.  The patch also adds a couple
more columns to pg_stat_bgwriter to help measure the effectiveness of the
bgwriter.

Greg Smith, building on his own work and ideas from several other people,
in particular a much older patch from Itagaki Takahiro.

This is problematic for the autovac launcher when there are many databases,
so we keep data for a full second before reading it again.

table, by allocating just enough for a hardcoded number of dead tuples per
page.  The current estimate is 200 dead tuples per page.

Per reports from Jeff Amiel, Erik Jones and Marko Kreen, and subsequent
discussion.
CVS: ----------------------------------------------------------------------
CVS: Enter Log.  Lines beginning with `CVS:' are removed automatically
CVS:
CVS: Committing in .
CVS:
CVS: Modified Files:
CVS: 	commands/vacuumlazy.c
CVS: ----------------------------------------------------------------------

* stats_start_collector goes away; we always start the collector process,
unless prevented by a problem with setting up the stats UDP socket.

* stats_reset_on_server_start goes away; it seems useless in view of the
availability of pg_stat_reset().

* stats_block_level and stats_row_level are merged into a single variable
"track_counts", which controls all reports sent to the collector process.

* stats_command_string is renamed to track_activities.

* log_autovacuum is renamed to log_autovacuum_min_duration to better reflect
its meaning.

The log_autovacuum change is not a compatibility issue since it didn't exist
before 8.3 anyway.  The other changes need to be release-noted.

produces text it is an encoding hole and if not it's incompatible
with the spec, whatever the spec means (which we're not sure about anyway).

lookup objects by OID.  Per gripe from nikitathespider.

the .bat files will be altered to become tiny wrappers for these scripts,
and one or two other .bat files will disappear.

pg_stat_activity.  Per gripe from Jim Nasby.

later than latestCompletedXid, per Florian Pflug.  Also some minor
improvements in the XIDCACHE_DEBUG code --- make sure each call of
TransactionIdIsInProgress is counted one way or another.

out at erratic times, because it is creating a totally unacceptable level
of noise in our buildfarm results.  This patch can be reverted when and if
the code is fixed to not issue notices during cache reload events.

(because they are uncorrelated with the immediate parent query).  We were
charging the full run cost to the parent node, disregarding the fact that
only one row need be fetched for EXISTS.  While this would only be a
cosmetic issue in most cases, it might possibly affect planning outcomes
if the parent query were itself a subquery to some upper query.
Per recent discussion with Steve Crawford.

calls. Fixes complaint fron Hannes Eder, whose environment found a different
dir program.

syslog and eventlog severity levels, per suggestion from Josh Drake.
Also, some wordsmithing for the csvlog documentation.

per ITAGAKI Takahiro.  Also, rewrite syslogger_forkexec() in hopes of
eliminating the confusion in the first place.

uses of PG_DETOAST_DATUM_SLICE, but it's clearly trouble waiting to
happen.

buildfarm member grebe, I see no reason to revert the 1-byte-header-friendly
changes I made in varlena.c.  Instead, tweak the code a little bit to
get more advantage out of that.

malloc returns NULL for malloc(0).  Defend against that case.

character encodings that doesn't involve calling lower(). This should
cure the performance regression in this case complained of by Guillaume
Smet. It still leaves the horrid performance for multi-byte encodings
introduced in 8.2, but there's no obvious solution for that in sight.

demonstrably necessary for text_substring() since regexp_split functions
may pass it such a value; and we might as well convert the whole file
at once.  Per buildfarm results (though I wonder why most machines aren't
showing a failure).

to not cause needless copying of text datums that have 1-byte headers.
Greg Stark, in response to performance gripe from Guillaume Smet and
ITAGAKI Takahiro.

unpruned XMAX in its header.  At the cost of 4 bytes per page, this keeps us
from performing heap_page_prune when there's no chance of pruning anything.
Seems to be necessary per Heikki's preliminary performance testing.

TransactionIdDidAbort, when handling the case that xmin is one of the current
transaction's XIDs and the tuple has been deleted.  xmax must also be one of
the current transaction's XIDs, since no one else can see it yet, and it's
cheaper to look at local state than shared state to find out if xmax aborted.
Per an idea of Heikki's.

For XIDs of our own transaction and subtransactions, it's cheaper to ask
TransactionIdIsCurrentTransactionId() than to look in shared memory.
Also, the xids[] work array is always the same size within any given
process, so malloc it just once instead of doing a palloc/pfree on every
call; aside from being faster this lets us get rid of some goto's, since
we no longer have any end-of-function pfree to do.  Both ideas by Heikki.

it ought to know that you need -DLINUX_PROFILE on Linux.

has a bad habit of launching multiple threads within the backend and thereby
causing all kinds of havoc.  Fortunately, we don't need it, and recent Tcl
versions provide an easy way to disable it.  Diagnosis and fix by
Steve Marshall, Paul Bayer, and Doug Knight of WSI Corporation.

but got lost from the version committed to main tree.  Per Greg Stark.

truncates a table.  Introduces race condition, as shown by buildfarm
failures.

> * -Consider shrinking expired tuples to just their headers
> * -Allow heap reuse of UPDATEd rows if no indexed columns are changed,
>   and old and new versions are on the same heap page

Not needed anymore:

< * Reuse index tuples that point to heap tuples that are not visible to
<   anyone?