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SSI comment fixes and enhancements. Notably, document that the conflict-out

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flag actually means that the transaction has a conflict out to a transaction
that committed before the flagged transaction.

Kevin Grittner
This commit is contained in:
Heikki Linnakangas 2011-06-03 12:45:42 +03:00
parent 52caa355ee
commit c8630919e0
2 changed files with 17 additions and 6 deletions
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18
src/backend/storage/lmgr/predicate.c
View File

@ -245,6 +245,11 @@
#define SxactIsReadOnly(sxact) (((sxact)->flags & SXACT_FLAG_READ_ONLY) != 0)
#define SxactHasSummaryConflictIn(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_IN) != 0)
#define SxactHasSummaryConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_OUT) != 0)
/*
* The following macro actually means that the specified transaction has a
* conflict out *to a transaction which committed ahead of it*. It's hard
* to get that into a name of a reasonable length.
*/
#define SxactHasConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_CONFLICT_OUT) != 0)
#define SxactIsDeferrableWaiting(sxact) (((sxact)->flags & SXACT_FLAG_DEFERRABLE_WAITING) != 0)
#define SxactIsROSafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_SAFE) != 0)
@ -2708,7 +2713,7 @@ SetNewSxactGlobalXmin(void)
* up in some relatively timely fashion.
*
* If this transaction is committing and is holding any predicate locks,
* it must be added to a list of completed serializable transaction still
* it must be added to a list of completed serializable transactions still
* holding locks.
*/
void
@ -2753,12 +2758,13 @@ ReleasePredicateLocks(const bool isCommit)
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
/*
* We don't hold a lock here, assuming that TransactionId is atomic!
* We don't hold XidGenLock lock here, assuming that TransactionId is
* atomic!
*
* If this value is changing, we don't care that much whether we get the
* old or new value -- it is just used to determine how far
* GlobalSerizableXmin must advance before this transaction can be cleaned
* fully cleaned up. The worst that could happen is we wait for ome more
* GlobalSerizableXmin must advance before this transaction can be fully
* cleaned up. The worst that could happen is we wait for one more
* transaction to complete before freeing some RAM; correctness of visible
* behavior is not affected.
*/
@ -3860,8 +3866,8 @@ OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
* Because T2 must've committed first, there is no anomaly if:
* - the reader committed before T2
* - the writer committed before T2
* - the reader is a READ ONLY transaction and the reader was not
* concurrent with T2 (= reader acquired its snapshot after T2 committed)
* - the reader is a READ ONLY transaction and the reader was concurrent
* with T2 (= reader acquired its snapshot before T2 committed)
*/
if (!failure)
{

5
src/include/storage/predicate_internals.h
View File

@ -92,6 +92,11 @@ typedef struct SERIALIZABLEXACT
#define SXACT_FLAG_ROLLED_BACK 0x00000001
#define SXACT_FLAG_COMMITTED 0x00000002
/*
* The following flag actually means that the flagged transaction has a
* conflict out *to a transaction which committed ahead of it*. It's hard
* to get that into a name of a reasonable length.
*/
#define SXACT_FLAG_CONFLICT_OUT 0x00000004
#define SXACT_FLAG_READ_ONLY 0x00000008
#define SXACT_FLAG_DID_WRITE 0x00000010