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Convert [autovacuum_]vacuum_cost_delay into floating-point GUCs.

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This change makes it possible to specify sub-millisecond delays,
which work well on most modern platforms, though that was not true
when the cost-delay feature was designed.

To support this without breaking existing configuration entries,
improve guc.c to allow floating-point GUCs to have units.  Also,
allow "us" (microseconds) as an input/output unit for time-unit GUCs.
(It's not allowed as a base unit, at least not yet.)

Likewise change the autovacuum_vacuum_cost_delay reloption to be
floating-point; this forces a catversion bump because the layout of
StdRdOptions changes.

This patch doesn't in itself change the default values or allowed
ranges for these parameters, and it should not affect the behavior
for any already-allowed setting for them.

Discussion: https://postgr.es/m/1798.1552165479@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-03-10 15:01:39 -04:00
parent 28a65fc360
commit caf626b2cd
15 changed files with 242 additions and 157 deletions
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23
doc/src/sgml/config.sgml
View File

@ -91,7 +91,9 @@
<listitem>
<para>
Valid time units are <literal>ms</literal> (milliseconds),
Valid time units are
<literal>us</literal> (microseconds),
<literal>ms</literal> (milliseconds),
<literal>s</literal> (seconds), <literal>min</literal> (minutes),
<literal>h</literal> (hours), and <literal>d</literal> (days).
</para>
@ -1845,7 +1847,7 @@ include_dir 'conf.d'
<variablelist>
<varlistentry id="guc-vacuum-cost-delay" xreflabel="vacuum_cost_delay">
<term><varname>vacuum_cost_delay</varname> (<type>integer</type>)
<term><varname>vacuum_cost_delay</varname> (<type>floating point</type>)
<indexterm>
<primary><varname>vacuum_cost_delay</varname> configuration parameter</primary>
</indexterm>
@ -1856,18 +1858,19 @@ include_dir 'conf.d'
when the cost limit has been exceeded.
The default value is zero, which disables the cost-based vacuum
delay feature. Positive values enable cost-based vacuuming.
Note that on many systems, the effective resolution
of sleep delays is 10 milliseconds; setting
<varname>vacuum_cost_delay</varname> to a value that is
not a multiple of 10 might have the same results as setting it
to the next higher multiple of 10.
</para>
<para>
When using cost-based vacuuming, appropriate values for
<varname>vacuum_cost_delay</varname> are usually quite small, perhaps
10 or 20 milliseconds. Adjusting vacuum's resource consumption
is best done by changing the other vacuum cost parameters.
less than 1 millisecond. While <varname>vacuum_cost_delay</varname>
can be set to fractional-millisecond values, such delays may not be
measured accurately on older platforms. On such platforms,
increasing <command>VACUUM</command>'s throttled resource consumption
above what you get at 1ms will require changing the other vacuum cost
parameters. You should, nonetheless,
keep <varname>vacuum_cost_delay</varname> as small as your platform
will consistently measure; large delays are not helpful.
</para>
</listitem>
</varlistentry>
@ -7020,7 +7023,7 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</varlistentry>
<varlistentry id="guc-autovacuum-vacuum-cost-delay" xreflabel="autovacuum_vacuum_cost_delay">
<term><varname>autovacuum_vacuum_cost_delay</varname> (<type>integer</type>)
<term><varname>autovacuum_vacuum_cost_delay</varname> (<type>floating point</type>)
<indexterm>
<primary><varname>autovacuum_vacuum_cost_delay</varname> configuration parameter</primary>
</indexterm>

2
doc/src/sgml/ref/create_table.sgml
View File

@ -1385,7 +1385,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</varlistentry>
<varlistentry>
<term><literal>autovacuum_vacuum_cost_delay</literal>, <literal>toast.autovacuum_vacuum_cost_delay</literal> (<type>integer</type>)</term>
<term><literal>autovacuum_vacuum_cost_delay</literal>, <literal>toast.autovacuum_vacuum_cost_delay</literal> (<type>floating point</type>)</term>
<listitem>
<para>
Per-table value for <xref linkend="guc-autovacuum-vacuum-cost-delay"/>