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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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5
src/backend/access/transam/xlogreader.c
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@ -1197,6 +1197,7 @@ DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, char **errormsg)
state->decoded_record = record;
state->record_origin = InvalidRepOriginId;
state->toplevel_xid = InvalidTransactionId;
ptr = (char *) record;
ptr += SizeOfXLogRecord;
@ -1235,6 +1236,10 @@ DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, char **errormsg)
{
COPY_HEADER_FIELD(&state->record_origin, sizeof(RepOriginId));
}
else if (block_id == XLR_BLOCK_ID_TOPLEVEL_XID)
{
COPY_HEADER_FIELD(&state->toplevel_xid, sizeof(TransactionId));
}
else if (block_id <= XLR_MAX_BLOCK_ID)
{
/* XLogRecordBlockHeader */