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Remove backwards compat ugliness in snapbuild.c. 

In 955a684e04 we fixed a bug in initial snapshot creation. In the
course of which several members of struct SnapBuild were obsoleted. As
SnapBuild is serialized to disk we couldn't change the memory layout.

Unfortunately I subsequently forgot about removing the backward compat
gunk, but luckily Heikki just reminded me.

This commit bumps SNAPBUILD_VERSION, therefore breaking existing
slots (which is fine in a major release).

Author: Andres Freund
Reminded-By: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/c94be044-818f-15e3-1ad3-7a7ae2dfed0a@iki.fi
This commit is contained in:
Andres Freund 2021-02-15 16:57:47 -08:00
parent 0e52903128
commit a975ff4980
1 changed files with 18 additions and 85 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

103
src/backend/replication/logical/snapbuild.c
View File

@ -189,24 +189,11 @@ struct SnapBuild
ReorderBuffer *reorder;
/*
* Outdated: This struct isn't used for its original purpose anymore, but
* can't be removed / changed in a minor version, because it's stored
* on-disk.
* TransactionId at which the next phase of initial snapshot building will
* happen. InvalidTransactionId if not known (i.e. SNAPBUILD_START), or
* when no next phase necessary (SNAPBUILD_CONSISTENT).
*/
struct
{
/*
* NB: This field is misused, until a major version can break on-disk
* compatibility. See SnapBuildNextPhaseAt() /
* SnapBuildStartNextPhaseAt().
*/
TransactionId was_xmin;
TransactionId was_xmax;
size_t was_xcnt; /* number of used xip entries */
size_t was_xcnt_space; /* allocated size of xip */
TransactionId *was_xip; /* running xacts array, xidComparator-sorted */
} was_running;
TransactionId next_phase_at;
/*
* Array of transactions which could have catalog changes that committed
@ -272,34 +259,6 @@ static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutof
static void SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn);
static bool SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn);
/*
* Return TransactionId after which the next phase of initial snapshot
* building will happen.
*/
static inline TransactionId
SnapBuildNextPhaseAt(SnapBuild *builder)
{
/*
* For backward compatibility reasons this has to be stored in the wrongly
* named field. Will be fixed in next major version.
*/
return builder->was_running.was_xmax;
}
/*
* Set TransactionId after which the next phase of initial snapshot building
* will happen.
*/
static inline void
SnapBuildStartNextPhaseAt(SnapBuild *builder, TransactionId at)
{
/*
* For backward compatibility reasons this has to be stored in the wrongly
* named field. Will be fixed in next major version.
*/
builder->was_running.was_xmax = at;
}
/*
* Allocate a new snapshot builder.
*
@ -728,7 +687,7 @@ SnapBuildProcessChange(SnapBuild *builder, TransactionId xid, XLogRecPtr lsn)
* we got into the SNAPBUILD_FULL_SNAPSHOT state.
*/
if (builder->state < SNAPBUILD_CONSISTENT &&
TransactionIdPrecedes(xid, SnapBuildNextPhaseAt(builder)))
TransactionIdPrecedes(xid, builder->next_phase_at))
return false;
/*
@ -945,7 +904,7 @@ SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid,
*/
if (builder->state == SNAPBUILD_START ||
(builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
TransactionIdPrecedes(xid, SnapBuildNextPhaseAt(builder))))
TransactionIdPrecedes(xid, builder->next_phase_at)))
{
/* ensure that only commits after this are getting replayed */
if (builder->start_decoding_at <= lsn)
@ -1267,7 +1226,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
Assert(TransactionIdIsNormal(builder->xmax));
builder->state = SNAPBUILD_CONSISTENT;
SnapBuildStartNextPhaseAt(builder, InvalidTransactionId);
builder->next_phase_at = InvalidTransactionId;
ereport(LOG,
(errmsg("logical decoding found consistent point at %X/%X",
@ -1299,7 +1258,7 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
else if (builder->state == SNAPBUILD_START)
{
builder->state = SNAPBUILD_BUILDING_SNAPSHOT;
SnapBuildStartNextPhaseAt(builder, running->nextXid);
builder->next_phase_at = running->nextXid;
/*
* 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
* be decoded. Switch to FULL_SNAPSHOT.
*/
else if (builder->state == SNAPBUILD_BUILDING_SNAPSHOT &&
TransactionIdPrecedesOrEquals(SnapBuildNextPhaseAt(builder),
TransactionIdPrecedesOrEquals(builder->next_phase_at,
running->oldestRunningXid))
{
builder->state = SNAPBUILD_FULL_SNAPSHOT;
SnapBuildStartNextPhaseAt(builder, running->nextXid);
builder->next_phase_at = running->nextXid;
ereport(LOG,
(errmsg("logical decoding found initial consistent point at %X/%X",
@ -1356,11 +1315,11 @@ SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *runn
* collected. Switch to CONSISTENT.
*/
else if (builder->state == SNAPBUILD_FULL_SNAPSHOT &&
TransactionIdPrecedesOrEquals(SnapBuildNextPhaseAt(builder),
TransactionIdPrecedesOrEquals(builder->next_phase_at,
running->oldestRunningXid))
{
builder->state = SNAPBUILD_CONSISTENT;
SnapBuildStartNextPhaseAt(builder, InvalidTransactionId);
builder->next_phase_at = InvalidTransactionId;
ereport(LOG,
(errmsg("logical decoding found consistent point at %X/%X",
@ -1463,7 +1422,7 @@ typedef struct SnapBuildOnDisk
offsetof(SnapBuildOnDisk, version)
#define SNAPBUILD_MAGIC 0x51A1E001
#define SNAPBUILD_VERSION 2
#define SNAPBUILD_VERSION 3
/*
* Store/Load a snapshot from disk, depending on the snapshot builder's state.
@ -1508,6 +1467,9 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
if (builder->state < SNAPBUILD_CONSISTENT)
return;
/* consistent snapshots have no next phase */
Assert(builder->next_phase_at == InvalidTransactionId);
/*
* We identify snapshots by the LSN they are valid for. We don't need to
* include timelines in the name as each LSN maps to exactly one timeline
@ -1596,9 +1558,6 @@ SnapBuildSerialize(SnapBuild *builder, XLogRecPtr lsn)
&ondisk->builder,
sizeof(SnapBuild));
/* there shouldn't be any running xacts */
Assert(builder->was_running.was_xcnt == 0);
/* copy committed xacts */
sz = sizeof(TransactionId) * builder->committed.xcnt;
memcpy(ondisk_c, builder->committed.xip, sz);
@ -1801,34 +1760,6 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
}
COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
/* restore running xacts (dead, but kept for backward compat) */
sz = sizeof(TransactionId) * ondisk.builder.was_running.was_xcnt_space;
ondisk.builder.was_running.was_xip =
MemoryContextAllocZero(builder->context, sz);
pgstat_report_wait_start(WAIT_EVENT_SNAPBUILD_READ);
readBytes = read(fd, ondisk.builder.was_running.was_xip, sz);
pgstat_report_wait_end();
if (readBytes != sz)
{
int save_errno = errno;
CloseTransientFile(fd);
if (readBytes < 0)
{
errno = save_errno;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read file \"%s\": %m", path)));
}
else
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("could not read file \"%s\": read %d of %zu",
path, readBytes, sz)));
}
COMP_CRC32C(checksum, ondisk.builder.was_running.was_xip, sz);
/* restore committed xacts information */
sz = sizeof(TransactionId) * ondisk.builder.committed.xcnt;
ondisk.builder.committed.xip = MemoryContextAllocZero(builder->context, sz);
@ -1890,6 +1821,8 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
if (TransactionIdPrecedes(ondisk.builder.xmin, builder->initial_xmin_horizon))
goto snapshot_not_interesting;
/* consistent snapshots have no next phase */
Assert(ondisk.builder.next_phase_at == InvalidTransactionId);
/* ok, we think the snapshot is sensible, copy over everything important */
builder->xmin = ondisk.builder.xmin;