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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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24
src/backend/access/transam/xlogutils.c
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@@ -783,10 +783,10 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa
}
}
/* openSegment callback for WALRead */
static int
wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext * segcxt,
TimeLineID *tli_p)
/* XLogReaderRoutine->segment_open callback for local pg_wal files */
int
wal_segment_open(XLogReaderState *state, XLogSegNo nextSegNo,
WALSegmentContext *segcxt, TimeLineID *tli_p)
{
TimeLineID tli = *tli_p;
char path[MAXPGPATH];
@@ -811,8 +811,17 @@ wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext * segcxt,
return -1; /* keep compiler quiet */
}
/* stock XLogReaderRoutine->segment_close callback */
void
wal_segment_close(XLogReaderState *state)
{
close(state->seg.ws_file);
/* need to check errno? */
state->seg.ws_file = -1;
}
/*
* read_page callback for reading local xlog files
* XLogReaderRoutine->page_read callback for reading local xlog files
*
* Public because it would likely be very helpful for someone writing another
* output method outside walsender, e.g. in a bgworker.
@@ -937,8 +946,9 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
* as 'count', read the whole page anyway. It's guaranteed to be
* zero-padded up to the page boundary if it's incomplete.
*/
if (!WALRead(cur_page, targetPagePtr, XLOG_BLCKSZ, tli, &state->seg,
&state->segcxt, wal_segment_open, &errinfo))
if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
&state->seg, &state->segcxt,
&errinfo))
WALReadRaiseError(&errinfo);
/* number of valid bytes in the buffer */