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Immediately WAL-log subtransaction and top-level XID association.

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The logical decoding infrastructure needs to know which top-level
transaction the subxact belongs to, in order to decode all the
changes. Until now that might be delayed until commit, due to the
caching (GPROC_MAX_CACHED_SUBXIDS), preventing features requiring
incremental decoding.

So we also write the assignment info into WAL immediately, as part
of the next WAL record (to minimize overhead) only when wal_level=logical.
We can not remove the existing XLOG_XACT_ASSIGNMENT WAL as that is
required for avoiding overflow in the hot standby snapshot.

Bump XLOG_PAGE_MAGIC, since this introduces XLR_BLOCK_ID_TOPLEVEL_XID.

Author: Tomas Vondra, Dilip Kumar, Amit Kapila
Reviewed-by: Amit Kapila
Tested-by: Neha Sharma and Mahendra Singh Thalor
Discussion: https://postgr.es/m/688b0b7f-2f6c-d827-c27b-216a8e3ea700@2ndquadrant.com
This commit is contained in:
Amit Kapila
2020-07-20 08:48:26 +05:30
parent d05b172a76
commit 0bead9af48
9 changed files with 108 additions and 24 deletions
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44
src/backend/replication/logical/decode.c
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@ -94,11 +94,27 @@ void
LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *record)
{
XLogRecordBuffer buf;
TransactionId txid;
buf.origptr = ctx->reader->ReadRecPtr;
buf.endptr = ctx->reader->EndRecPtr;
buf.record = record;
txid = XLogRecGetTopXid(record);
/*
* If the top-level xid is valid, we need to assign the subxact to the
* top-level xact. We need to do this for all records, hence we do it
* before the switch.
*/
if (TransactionIdIsValid(txid))
{
ReorderBufferAssignChild(ctx->reorder,
txid,
record->decoded_record->xl_xid,
buf.origptr);
}
/* cast so we get a warning when new rmgrs are added */
switch ((RmgrId) XLogRecGetRmid(record))
{
@ -216,13 +232,8 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
/*
* If the snapshot isn't yet fully built, we cannot decode anything, so
* bail out.
*
* However, it's critical to process XLOG_XACT_ASSIGNMENT records even
* when the snapshot is being built: it is possible to get later records
* that require subxids to be properly assigned.
*/
if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT &&
info != XLOG_XACT_ASSIGNMENT)
if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
return;
switch (info)
@ -264,22 +275,13 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
break;
}
case XLOG_XACT_ASSIGNMENT:
{
xl_xact_assignment *xlrec;
int i;
TransactionId *sub_xid;
xlrec = (xl_xact_assignment *) XLogRecGetData(r);
sub_xid = &xlrec->xsub[0];
for (i = 0; i < xlrec->nsubxacts; i++)
{
ReorderBufferAssignChild(reorder, xlrec->xtop,
*(sub_xid++), buf->origptr);
}
break;
}
/*
* We assign subxact to the toplevel xact while processing each
* record if required. So, we don't need to do anything here.
* See LogicalDecodingProcessRecord.
*/
break;
case XLOG_XACT_PREPARE:
/*