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Code review for auto-tuned effective_cache_size.

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Fix integer overflow issue noted by Magnus Hagander, as well as a bunch
of other infelicities in commit ee1e5662d8
and its unreasonably large number of followups.
This commit is contained in:
Tom Lane
2014-01-27 00:05:49 -05:00
parent dd515d4082
commit 2850896961
7 changed files with 78 additions and 68 deletions
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28
doc/src/sgml/config.sgml
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@ -2974,17 +2974,9 @@ include 'filename'
<listitem>
<para>
Sets the planner's assumption about the effective size of the
disk cache that is available to a single query. The default
setting of -1 selects a size equal to four times the size of <xref
linkend="guc-shared-buffers">, but not less than the size of one
shared buffer page, typically <literal>8kB</literal>. This value
can be set manually if the automatic choice is too large or too
small.
</para>
<para>
This value is factored into estimates of the cost of using an index;
a higher value makes it more likely index scans will be used, a
disk cache that is available to a single query. This is
factored into estimates of the cost of using an index; a
higher value makes it more likely index scans will be used, a
lower value makes it more likely sequential scans will be
used. When setting this parameter you should consider both
<productname>PostgreSQL</productname>'s shared buffers and the
@ -2996,10 +2988,16 @@ include 'filename'
memory allocated by <productname>PostgreSQL</productname>, nor
does it reserve kernel disk cache; it is used only for estimation
purposes. The system also does not assume data remains in
the disk cache between queries. The auto-tuning
selected by the default setting of -1 should give reasonable
results if this database cluster can utilize most of the memory
on this server.
the disk cache between queries.
</para>
<para>
If <varname>effective_cache_size</> is set to -1, which is the
default, the value is replaced by an automatically selected value,
currently four times the size of <xref linkend="guc-shared-buffers">.
For recommended settings of <varname>shared_buffers</>, this should
give reasonable results if this database cluster can use most of the
memory on the server.
</para>
</listitem>
</varlistentry>