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Rework XLogReader callback system

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Code review for 0dc8ead463, prompted by a bug closed by 91c40548d5.

XLogReader's system for opening and closing segments had gotten too
complicated, with callbacks being passed at both the XLogReaderAllocate
level (read_page) as well as at the WALRead level (segment_open).  This
was confusing and hard to follow, so restructure things so that these
callbacks are passed together at XLogReaderAllocate time, and add
another callback to the set (segment_close) to make it a coherent whole.
Also, ensure XLogReaderState is an argument to all the callbacks, so
that they can grab at the ->private data if necessary.

Document the whole arrangement more clearly.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20200422175754.GA19858@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2020-05-08 15:30:34 -04:00
parent 871696ba20
commit b060dbe000
13 changed files with 214 additions and 113 deletions
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10
src/backend/access/transam/xlog.c
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@ -1223,7 +1223,7 @@ XLogInsertRecord(XLogRecData *rdata,
if (!debug_reader)
debug_reader = XLogReaderAllocate(wal_segment_size, NULL,
NULL, NULL);
XL_ROUTINE(), NULL);
if (!debug_reader)
{
@ -6478,8 +6478,12 @@ StartupXLOG(void)
/* Set up XLOG reader facility */
MemSet(&private, 0, sizeof(XLogPageReadPrivate));
xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
&XLogPageRead, &private);
xlogreader =
XLogReaderAllocate(wal_segment_size, NULL,
XL_ROUTINE(.page_read = &XLogPageRead,
.segment_open = NULL,
.segment_close = wal_segment_close),
&private);
if (!xlogreader)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),