WAL log only the actual GID instead of the entire GIDSIZE data

While GIDSIZE is set to quite high (actually, in XL its even more than 200
bytes currently defined in PG), in practice, the GID will be much smaller in
length. So instead of WAL logging the entire GIDSIZE data, we only log the
actual GID string. This shows considerable improvement for XL

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 2a5d43ed9caf0455eb12132e1c82a57e6f793a85..3feeb74de14a9a1176f1fdb4973f201b19112278 100644 (file)
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -889,7 +889,7 @@ typedef struct TwoPhaseFileHeader
        int32           nabortrels;             /* number of delete-on-abort rels */
        int32           ninvalmsgs;             /* number of cache invalidation messages */
        bool            initfileinval;  /* does relcache init file need invalidation? */
-       char            gid[GIDSIZE];   /* GID for transaction */
+       uint32          gidlen;                 /* length of the GID */
 } TwoPhaseFileHeader;
 
 /*
@@ -1000,9 +1000,10 @@ StartPrepare(GlobalTransaction gxact)
        hdr.nabortrels = smgrGetPendingDeletes(false, &abortrels);
        hdr.ninvalmsgs = xactGetCommittedInvalidationMessages(&invalmsgs,
                                                                                                                  &hdr.initfileinval);
-       StrNCpy(hdr.gid, gxact->gid, GIDSIZE);
+       hdr.gidlen = strlen(gxact->gid);
 
        save_state_data(&hdr, sizeof(TwoPhaseFileHeader));
+       save_state_data(gxact->gid, hdr.gidlen);
 
        /*
         * Add the additional info about subxacts, deletable files and cache
@@ -1424,6 +1425,7 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
        hdr = (TwoPhaseFileHeader *) buf;
        Assert(TransactionIdEquals(hdr->xid, xid));
        bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
+       bufptr += MAXALIGN(hdr->gidlen);
        children = (TransactionId *) bufptr;
        bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
        commitrels = (RelFileNode *) bufptr;
@@ -2004,6 +2006,7 @@ RecoverPreparedTransactions(void)
                        TwoPhaseFileHeader *hdr;
                        TransactionId *subxids;
                        GlobalTransaction gxact;
+                       const char      *gid;
                        int                     i;
 
                        xid = (TransactionId) strtoul(clde->d_name, NULL, 16);
@@ -2036,6 +2039,8 @@ RecoverPreparedTransactions(void)
                        hdr = (TwoPhaseFileHeader *) buf;
                        Assert(TransactionIdEquals(hdr->xid, xid));
                        bufptr = buf + MAXALIGN(sizeof(TwoPhaseFileHeader));
+                       gid = (const char *) bufptr;
+                       bufptr += MAXALIGN(hdr->gidlen);
                        subxids = (TransactionId *) bufptr;
                        bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
                        bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode));
@@ -2071,7 +2076,7 @@ RecoverPreparedTransactions(void)
                         * negligible (especially since we know the state file has already
                         * been fsynced).
                         */
-                       gxact = MarkAsPreparing(xid, hdr->gid,
+                       gxact = MarkAsPreparing(xid, gid,
                                                                        hdr->prepared_at,
                                                                        hdr->owner, hdr->database);
                        GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);