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Commita975ff4

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Remove backwards compat ugliness in snapbuild.c.
In955a684 we fixed a bug in initial snapshot creation. In thecourse of which several members of struct SnapBuild were obsoleted. AsSnapBuild is serialized to disk we couldn't change the memory layout.Unfortunately I subsequently forgot about removing the backward compatgunk, but luckily Heikki just reminded me.This commit bumps SNAPBUILD_VERSION, therefore breaking existingslots (which is fine in a major release).Author: Andres FreundReminded-By: Heikki Linnakangas <hlinnaka@iki.fi>Discussion:https://postgr.es/m/c94be044-818f-15e3-1ad3-7a7ae2dfed0a@iki.fi
1 parent0e52903 commita975ff4

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+18
-85
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1 file changed

+18
-85
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‎src/backend/replication/logical/snapbuild.c

Lines changed: 18 additions & 85 deletions
Original file line numberDiff line numberDiff line change
@@ -189,24 +189,11 @@ struct SnapBuild
189189
ReorderBuffer*reorder;
190190

191191
/*
192-
*Outdated: This struct isn't used for its original purpose anymore, but
193-
*can't be removed / changed in a minor version, because it's stored
194-
*on-disk.
192+
*TransactionId at which the next phase of initial snapshot building will
193+
*happen. InvalidTransactionId if not known (i.e. SNAPBUILD_START), or
194+
*when no next phase necessary (SNAPBUILD_CONSISTENT).
195195
*/
196-
struct
197-
{
198-
/*
199-
* NB: This field is misused, until a major version can break on-disk
200-
* compatibility. See SnapBuildNextPhaseAt() /
201-
* SnapBuildStartNextPhaseAt().
202-
*/
203-
TransactionIdwas_xmin;
204-
TransactionIdwas_xmax;
205-
206-
size_twas_xcnt;/* number of used xip entries */
207-
size_twas_xcnt_space;/* allocated size of xip */
208-
TransactionId*was_xip;/* running xacts array, xidComparator-sorted */
209-
}was_running;
196+
TransactionIdnext_phase_at;
210197

211198
/*
212199
* Array of transactions which could have catalog changes that committed
@@ -272,34 +259,6 @@ static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutof
272259
staticvoidSnapBuildSerialize(SnapBuild*builder,XLogRecPtrlsn);
273260
staticboolSnapBuildRestore(SnapBuild*builder,XLogRecPtrlsn);
274261

275-
/*
276-
* Return TransactionId after which the next phase of initial snapshot
277-
* building will happen.
278-
*/
279-
staticinlineTransactionId
280-
SnapBuildNextPhaseAt(SnapBuild*builder)
281-
{
282-
/*
283-
* For backward compatibility reasons this has to be stored in the wrongly
284-
* named field. Will be fixed in next major version.
285-
*/
286-
returnbuilder->was_running.was_xmax;
287-
}
288-
289-
/*
290-
* Set TransactionId after which the next phase of initial snapshot building
291-
* will happen.
292-
*/
293-
staticinlinevoid
294-
SnapBuildStartNextPhaseAt(SnapBuild*builder,TransactionIdat)
295-
{
296-
/*
297-
* For backward compatibility reasons this has to be stored in the wrongly
298-
* named field. Will be fixed in next major version.
299-
*/
300-
builder->was_running.was_xmax=at;
301-
}
302-
303262
/*
304263
* Allocate a new snapshot builder.
305264
*
@@ -728,7 +687,7 @@ SnapBuildProcessChange(SnapBuild *builder, TransactionId xid, XLogRecPtr lsn)
728687
* we got into the SNAPBUILD_FULL_SNAPSHOT state.
729688
*/
730689
if (builder->state<SNAPBUILD_CONSISTENT&&
731-
TransactionIdPrecedes(xid,SnapBuildNextPhaseAt(builder)))
690+
TransactionIdPrecedes(xid,builder->next_phase_at))
732691
return false;
733692

734693
/*
@@ -945,7 +904,7 @@ SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid,
945904
*/
946905
if (builder->state==SNAPBUILD_START||
947906
(builder->state==SNAPBUILD_BUILDING_SNAPSHOT&&
948-
TransactionIdPrecedes(xid,SnapBuildNextPhaseAt(builder))))
907+
TransactionIdPrecedes(xid,builder->next_phase_at)))
949908
{
950909
/* ensure that only commits after this are getting replayed */
951910
if (builder->start_decoding_at <=lsn)
@@ -1267,7 +1226,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
12671226
Assert(TransactionIdIsNormal(builder->xmax));
12681227

12691228
builder->state=SNAPBUILD_CONSISTENT;
1270-
SnapBuildStartNextPhaseAt(builder,InvalidTransactionId);
1229+
builder->next_phase_at=InvalidTransactionId;
12711230

12721231
ereport(LOG,
12731232
(errmsg("logical decoding found consistent point at %X/%X",
@@ -1299,7 +1258,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
12991258
elseif (builder->state==SNAPBUILD_START)
13001259
{
13011260
builder->state=SNAPBUILD_BUILDING_SNAPSHOT;
1302-
SnapBuildStartNextPhaseAt(builder,running->nextXid);
1261+
builder->next_phase_at=running->nextXid;
13031262

13041263
/*
13051264
* Start with an xmin/xmax that's correct for future, when all the
@@ -1331,11 +1290,11 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
13311290
* be decoded. Switch to FULL_SNAPSHOT.
13321291
*/
13331292
elseif (builder->state==SNAPBUILD_BUILDING_SNAPSHOT&&
1334-
TransactionIdPrecedesOrEquals(SnapBuildNextPhaseAt(builder),
1293+
TransactionIdPrecedesOrEquals(builder->next_phase_at,
13351294
running->oldestRunningXid))
13361295
{
13371296
builder->state=SNAPBUILD_FULL_SNAPSHOT;
1338-
SnapBuildStartNextPhaseAt(builder,running->nextXid);
1297+
builder->next_phase_at=running->nextXid;
13391298

13401299
ereport(LOG,
13411300
(errmsg("logical decoding found initial consistent point at %X/%X",
@@ -1356,11 +1315,11 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
13561315
* collected. Switch to CONSISTENT.
13571316
*/
13581317
elseif (builder->state==SNAPBUILD_FULL_SNAPSHOT&&
1359-
TransactionIdPrecedesOrEquals(SnapBuildNextPhaseAt(builder),
1318+
TransactionIdPrecedesOrEquals(builder->next_phase_at,
13601319
running->oldestRunningXid))
13611320
{
13621321
builder->state=SNAPBUILD_CONSISTENT;
1363-
SnapBuildStartNextPhaseAt(builder,InvalidTransactionId);
1322+
builder->next_phase_at=InvalidTransactionId;
13641323

13651324
ereport(LOG,
13661325
(errmsg("logical decoding found consistent point at %X/%X",
@@ -1463,7 +1422,7 @@ typedef struct SnapBuildOnDisk
14631422
offsetof(SnapBuildOnDisk, version)
14641423

14651424
#defineSNAPBUILD_MAGIC 0x51A1E001
1466-
#defineSNAPBUILD_VERSION2
1425+
#defineSNAPBUILD_VERSION3
14671426

14681427
/*
14691428
* Store/Load a snapshot from disk, depending on the snapshot builder's state.
@@ -1508,6 +1467,9 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
15081467
if (builder->state<SNAPBUILD_CONSISTENT)
15091468
return;
15101469

1470+
/* consistent snapshots have no next phase */
1471+
Assert(builder->next_phase_at==InvalidTransactionId);
1472+
15111473
/*
15121474
* We identify snapshots by the LSN they are valid for. We don't need to
15131475
* include timelines in the name as each LSN maps to exactly one timeline
@@ -1596,9 +1558,6 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
15961558
&ondisk->builder,
15971559
sizeof(SnapBuild));
15981560

1599-
/* there shouldn't be any running xacts */
1600-
Assert(builder->was_running.was_xcnt==0);
1601-
16021561
/* copy committed xacts */
16031562
sz=sizeof(TransactionId)*builder->committed.xcnt;
16041563
memcpy(ondisk_c,builder->committed.xip,sz);
@@ -1801,34 +1760,6 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
18011760
}
18021761
COMP_CRC32C(checksum,&ondisk.builder,sizeof(SnapBuild));
18031762

1804-
/* restore running xacts (dead, but kept for backward compat) */
1805-
sz=sizeof(TransactionId)*ondisk.builder.was_running.was_xcnt_space;
1806-
ondisk.builder.was_running.was_xip=
1807-
MemoryContextAllocZero(builder->context,sz);
1808-
pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
1809-
readBytes=read(fd,ondisk.builder.was_running.was_xip,sz);
1810-
pgstat_report_wait_end();
1811-
if (readBytes!=sz)
1812-
{
1813-
intsave_errno=errno;
1814-
1815-
CloseTransientFile(fd);
1816-
1817-
if (readBytes<0)
1818-
{
1819-
errno=save_errno;
1820-
ereport(ERROR,
1821-
(errcode_for_file_access(),
1822-
errmsg("could not read file \"%s\": %m",path)));
1823-
}
1824-
else
1825-
ereport(ERROR,
1826-
(errcode(ERRCODE_DATA_CORRUPTED),
1827-
errmsg("could not read file \"%s\": read %d of %zu",
1828-
path,readBytes,sz)));
1829-
}
1830-
COMP_CRC32C(checksum,ondisk.builder.was_running.was_xip,sz);
1831-
18321763
/* restore committed xacts information */
18331764
sz=sizeof(TransactionId)*ondisk.builder.committed.xcnt;
18341765
ondisk.builder.committed.xip=MemoryContextAllocZero(builder->context,sz);
@@ -1890,6 +1821,8 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
18901821
if (TransactionIdPrecedes(ondisk.builder.xmin,builder->initial_xmin_horizon))
18911822
gotosnapshot_not_interesting;
18921823

1824+
/* consistent snapshots have no next phase */
1825+
Assert(ondisk.builder.next_phase_at==InvalidTransactionId);
18931826

18941827
/* ok, we think the snapshot is sensible, copy over everything important */
18951828
builder->xmin=ondisk.builder.xmin;

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