Re: increasing the default WAL segment size

From: Beena Emerson <memissemerson(at)gmail(dot)com>
To: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: increasing the default WAL segment size
Date: 2016-12-19 09:44:50
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Hello all,

Please find attached a patch to make wal segment size initdb configurable.

The attached patch removes --with-wal-segsize configure option and adds a
new initdb option --wal-segsize. The module initdb passes the wal-segsize
value into an environment variable which is used to overwrite the guc value
wal_ segment_size and set the internal variables : XLogSegSize and
XLOG_SEG_SIZE (xlog_internal.h). The default wal_segment_size is not
changed but I have increased the maximum size to 1GB.

Since XLOG_SEG_SIZE is now variable, it could not be used directly in
src/bin modules and few macros and few changes had to be made:
- in guc.c , remove GUC_UNIT_XSEGS which used XLOG_SEG_SIZE and
introduce show functions for the guc which used the unit (min_wal_size and
- For pg_basebackup, add new replication command SHOW_WAL_SEGSZ to fetch
the wal_segment_size in bytes.
- pg_controldata, pg_resetxlog, pg_rewind, fetch the xlog_seg_size from
the ControlFile.
- Since pg_xlogdump reads the wal files, it uses the file size to
determine the xlog_seg_size.
- In pg_test_fsync, a buffer of size XLOG_SEG_SIZE was created, filled
with random data and written to a temporary file to check for any
write/fsync error before performing the tests. Since it does not affect the
actual performance results, the XLOG_SEG_SIZE in the module is replaced
with the default value (16MB).

Please note that the documents are not updated in this patch.

Feedback and suggestions are welcome.

Beena Emerson

Have a Great Day!

Attachment Content-Type Size
initdb-walsegsize_v1.patch application/octet-stream 28.7 KB

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