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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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36
src/backend/replication/walsender.c
View File

@@ -54,8 +54,8 @@
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog_internal.h"
#include "access/xlogreader.h"
#include "access/xlogutils.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
@@ -248,8 +248,8 @@ static void LagTrackerWrite(XLogRecPtr lsn, TimestampTz local_flush_time);
static TimeOffset LagTrackerRead(int head, XLogRecPtr lsn, TimestampTz now);
static bool TransactionIdInRecentPast(TransactionId xid, uint32 epoch);
static int WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
TimeLineID *tli_p);
static int WalSndSegmentOpen(XLogReaderState *state, XLogSegNo nextSegNo,
WALSegmentContext *segcxt, TimeLineID *tli_p);
static void UpdateSpillStats(LogicalDecodingContext *ctx);
@@ -798,7 +798,8 @@ StartReplication(StartReplicationCmd *cmd)
}
/*
* read_page callback for logical decoding contexts, as a walsender process.
* XLogReaderRoutine->page_read callback for logical decoding contexts, as a
* walsender process.
*
* Inside the walsender we can do better than read_local_xlog_page,
* which has to do a plain sleep/busy loop, because the walsender's latch gets
@@ -832,7 +833,8 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
count = flushptr - targetPagePtr; /* part of the page available */
/* now actually read the data, we know it's there */
if (!WALRead(cur_page,
if (!WALRead(state,
cur_page,
targetPagePtr,
XLOG_BLCKSZ,
sendSeg->ws_tli, /* Pass the current TLI because only
@@ -840,7 +842,6 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
* TLI is needed. */
sendSeg,
sendCxt,
WalSndSegmentOpen,
&errinfo))
WALReadRaiseError(&errinfo);
@@ -1005,7 +1006,9 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
InvalidXLogRecPtr,
logical_read_xlog_page,
XL_ROUTINE(.page_read = logical_read_xlog_page,
.segment_open = WalSndSegmentOpen,
.segment_close = wal_segment_close),
WalSndPrepareWrite, WalSndWriteData,
WalSndUpdateProgress);
@@ -1168,7 +1171,9 @@ StartLogicalReplication(StartReplicationCmd *cmd)
*/
logical_decoding_ctx =
CreateDecodingContext(cmd->startpoint, cmd->options, false,
logical_read_xlog_page,
XL_ROUTINE(.page_read = logical_read_xlog_page,
.segment_open = WalSndSegmentOpen,
.segment_close = wal_segment_close),
WalSndPrepareWrite, WalSndWriteData,
WalSndUpdateProgress);
@@ -2441,9 +2446,10 @@ WalSndKill(int code, Datum arg)
SpinLockRelease(&walsnd->mutex);
}
/* walsender's openSegment callback for WALRead */
/* XLogReaderRoutine->segment_open callback */
static int
WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
WalSndSegmentOpen(XLogReaderState *state,
XLogSegNo nextSegNo, WALSegmentContext *segcxt,
TimeLineID *tli_p)
{
char path[MAXPGPATH];
@@ -2531,6 +2537,12 @@ XLogSendPhysical(void)
Size nbytes;
XLogSegNo segno;
WALReadError errinfo;
static XLogReaderState fake_xlogreader =
{
/* Fake xlogreader state for WALRead */
.routine.segment_open = WalSndSegmentOpen,
.routine.segment_close = wal_segment_close
};
/* If requested switch the WAL sender to the stopping state. */
if (got_STOPPING)
@@ -2748,7 +2760,8 @@ XLogSendPhysical(void)
enlargeStringInfo(&output_message, nbytes);
retry:
if (!WALRead(&output_message.data[output_message.len],
if (!WALRead(&fake_xlogreader,
&output_message.data[output_message.len],
startptr,
nbytes,
sendSeg->ws_tli, /* Pass the current TLI because only
@@ -2756,7 +2769,6 @@ retry:
* TLI is needed. */
sendSeg,
sendCxt,
WalSndSegmentOpen,
&errinfo))
WALReadRaiseError(&errinfo);