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Refactor XLogReadRecord(), adding XLogBeginRead() function.

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The signature of XLogReadRecord() required the caller to pass the starting
WAL position as argument, or InvalidXLogRecPtr to continue reading at the
end of previous record. That's slightly awkward to the callers, as most
of them don't want to randomly jump around in the WAL stream, but start
reading at one position and then read everything from that point onwards.
Remove the 'RecPtr' argument and add a new function XLogBeginRead() to
specify the starting position instead. That's more convenient for the
callers. Also, xlogreader holds state that is reset when you change the
starting position, so having a separate function for doing that feels like
a more natural fit.

This changes XLogFindNextRecord() function so that it doesn't reset the
xlogreader's state to what it was before the call anymore. Instead, it
positions the xlogreader to the found record, like XLogBeginRead().

Reviewed-by: Kyotaro Horiguchi, Alvaro Herrera
Discussion: https://www.postgresql.org/message-id/5382a7a3-debe-be31-c860-cb810c08f366%40iki.fi
This commit is contained in:
Heikki Linnakangas
2020-01-26 11:39:00 +02:00
parent 1001368497
commit 38a957316d
10 changed files with 102 additions and 97 deletions
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13
src/backend/replication/slotfuncs.c
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@@ -391,7 +391,6 @@ pg_logical_replication_slot_advance(XLogRecPtr moveto)
{
LogicalDecodingContext *ctx;
ResourceOwner old_resowner = CurrentResourceOwner;
XLogRecPtr startlsn;
XLogRecPtr retlsn;
PG_TRY();
@@ -411,7 +410,7 @@ pg_logical_replication_slot_advance(XLogRecPtr moveto)
* Start reading at the slot's restart_lsn, which we know to point to
* a valid record.
*/
startlsn = MyReplicationSlot->data.restart_lsn;
XLogBeginRead(ctx->reader, MyReplicationSlot->data.restart_lsn);
/* Initialize our return value in case we don't do anything */
retlsn = MyReplicationSlot->data.confirmed_flush;
@@ -420,10 +419,7 @@ pg_logical_replication_slot_advance(XLogRecPtr moveto)
InvalidateSystemCaches();
/* Decode at least one record, until we run out of records */
while ((!XLogRecPtrIsInvalid(startlsn) &&
startlsn < moveto) ||
(!XLogRecPtrIsInvalid(ctx->reader->EndRecPtr) &&
ctx->reader->EndRecPtr < moveto))
while (ctx->reader->EndRecPtr < moveto)
{
char *errm = NULL;
XLogRecord *record;
@@ -432,13 +428,10 @@ pg_logical_replication_slot_advance(XLogRecPtr moveto)
* Read records. No changes are generated in fast_forward mode,
* but snapbuilder/slot statuses are updated properly.
*/
record = XLogReadRecord(ctx->reader, startlsn, &errm);
record = XLogReadRecord(ctx->reader, &errm);
if (errm)
elog(ERROR, "%s", errm);
/* Read sequentially from now on */
startlsn = InvalidXLogRecPtr;
/*
* Process the record. Storage-level changes are ignored in
* fast_forward mode, but other modules (such as snapbuilder)