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Add wal_recycle and wal_init_zero GUCs.

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On at least ZFS, it can be beneficial to create new WAL files every
time and not to bother zero-filling them.  Since it's not clear which
other filesystems might benefit from one or both of those things,
add individual GUCs to control those two behaviors independently and
make only very general statements in the docs.

Author: Jerry Jelinek, with some adjustments by Thomas Munro
Reviewed-by: Alvaro Herrera, Andres Freund, Tomas Vondra, Robert Haas and others
Discussion: https://postgr.es/m/CACPQ5Fo00QR7LNAcd1ZjgoBi4y97%2BK760YABs0vQHH5dLdkkMA%40mail.gmail.com
This commit is contained in:
Thomas Munro
2019-04-02 14:37:14 +13:00
parent 4b82664156
commit 475861b261
5 changed files with 127 additions and 37 deletions
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35
doc/src/sgml/config.sgml
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@ -3590,6 +3590,41 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
</listitem>
</varlistentry>
<varlistentry id="guc-wal-init-zero" xreflabel="wal_init_zero">
<term><varname>wal_init_zero</varname> (<type>boolean</type>)
<indexterm>
<primary><varname>wal_init_zero</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
If set to <literal>on</literal> (the default), this option causes new
WAL files to be filled with zeroes. On some filesystems, this ensures
that space is allocated before we need to write WAL records. However,
<firstterm>Copy-On-Write</firstterm> (COW) filesystems may not benefit
from this technique, so the option is given to skip the unnecessary
work. If set to <literal>off</literal>, only the final byte is written
when the file is created so that it has the expected size.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-wal-recycle" xreflabel="wal_recycle">
<term><varname>wal_recycle</varname> (<type>boolean</type>)
<indexterm>
<primary><varname>wal_recycle</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
If set to <literal>on</literal> (the default), this option causes WAL
files to be recycled by renaming them, avoiding the need to create new
ones. On COW filesystems, it may be faster to create new ones, so the
option is given to disable this behavior.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-wal-sender-timeout" xreflabel="wal_sender_timeout">
<term><varname>wal_sender_timeout</varname> (<type>integer</type>)
<indexterm>