/* * GetTransactionSnapshot * Get the appropriate snapshot for a new query in a transaction. * * Note that the return value may point at static storage that will be modified * by future calls and by CommandCounterIncrement(). Callers should call * RegisterSnapshot or PushActiveSnapshot on the returned snap if it is to be * used very long. */ Snapshot GetTransactionSnapshot(void) { /* First call in transaction? */ if (!FirstSnapshotSet) { Assert(RegisteredSnapshots == 0); Assert(FirstXactSnapshot == NULL); /* * In transaction-snapshot mode, the first snapshot must live until * end of xact regardless of what the caller does with it, so we must * make a copy of it rather than returning CurrentSnapshotData * directly. Furthermore, if we're running in serializable mode, * predicate.c needs to wrap the snapshot fetch in its own processing. */ if (IsolationUsesXactSnapshot()) { /* First, create the snapshot in CurrentSnapshotData */ if (IsolationIsSerializable()) CurrentSnapshot = GetSerializableTransactionSnapshot(&CurrentSnapshotData); else CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); /* Make a saved copy */ CurrentSnapshot = CopySnapshot(CurrentSnapshot); FirstXactSnapshot = CurrentSnapshot; /* Mark it as "registered" in FirstXactSnapshot */ FirstXactSnapshot->regd_count++; RegisteredSnapshots++; } else CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); FirstSnapshotSet = true; return CurrentSnapshot; } if (IsolationUsesXactSnapshot()) return CurrentSnapshot; CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); return CurrentSnapshot; }
/* * GetTransactionSnapshot * Get the appropriate snapshot for a new query in a transaction. * * Note that the return value may point at static storage that will be modified * by future calls and by CommandCounterIncrement(). Callers should call * RegisterSnapshot or PushActiveSnapshot on the returned snap if it is to be * used very long. */ Snapshot GetTransactionSnapshot(void) { /* * Return historic snapshot if doing logical decoding. We'll never need a * non-historic transaction snapshot in this (sub-)transaction, so there's * no need to be careful to set one up for later calls to * GetTransactionSnapshot(). */ if (HistoricSnapshotActive()) { Assert(!FirstSnapshotSet); return HistoricSnapshot; } /* First call in transaction? */ if (!FirstSnapshotSet) { Assert(pairingheap_is_empty(&RegisteredSnapshots)); Assert(FirstXactSnapshot == NULL); if (IsInParallelMode()) elog(ERROR, "cannot take query snapshot during a parallel operation"); /* * In transaction-snapshot mode, the first snapshot must live until * end of xact regardless of what the caller does with it, so we must * make a copy of it rather than returning CurrentSnapshotData * directly. Furthermore, if we're running in serializable mode, * predicate.c needs to wrap the snapshot fetch in its own processing. */ if (IsolationUsesXactSnapshot()) { /* First, create the snapshot in CurrentSnapshotData */ if (IsolationIsSerializable()) CurrentSnapshot = GetSerializableTransactionSnapshot(&CurrentSnapshotData); else CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); /* Make a saved copy */ CurrentSnapshot = CopySnapshot(CurrentSnapshot); FirstXactSnapshot = CurrentSnapshot; /* Mark it as "registered" in FirstXactSnapshot */ FirstXactSnapshot->regd_count++; pairingheap_add(&RegisteredSnapshots, &FirstXactSnapshot->ph_node); } else CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); /* Don't allow catalog snapshot to be older than xact snapshot. */ CatalogSnapshotStale = true; FirstSnapshotSet = true; return CurrentSnapshot; } if (IsolationUsesXactSnapshot()) return CurrentSnapshot; /* Don't allow catalog snapshot to be older than xact snapshot. */ CatalogSnapshotStale = true; CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); return CurrentSnapshot; }
/* * GetTransactionSnapshot * Get the appropriate snapshot for a new query in a transaction. * * Note that the return value may point at static storage that will be modified * by future calls and by CommandCounterIncrement(). Callers should call * RegisterSnapshot or PushActiveSnapshot on the returned snap if it is to be * used very long. */ Snapshot GetTransactionSnapshot(void) { /* First call in transaction? */ if (!FirstSnapshotSet) { Assert(RegisteredSnapshots == 0); Assert(FirstXactSnapshot == NULL); /* * In transaction-snapshot mode, the first snapshot must live until * end of xact regardless of what the caller does with it, so we must * make a copy of it rather than returning CurrentSnapshotData * directly. Furthermore, if we're running in serializable mode, * predicate.c needs to wrap the snapshot fetch in its own processing. */ if (IsolationUsesXactSnapshot()) { /* First, create the snapshot in CurrentSnapshotData */ if (IsolationIsSerializable()) CurrentSnapshot = GetSerializableTransactionSnapshot(&CurrentSnapshotData); else CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); /* Make a saved copy */ CurrentSnapshot = CopySnapshot(CurrentSnapshot); FirstXactSnapshot = CurrentSnapshot; /* Mark it as "registered" in FirstXactSnapshot */ FirstXactSnapshot->regd_count++; RegisteredSnapshots++; } else CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); FirstSnapshotSet = true; return CurrentSnapshot; } if (IsolationUsesXactSnapshot()) { #ifdef PGXC /* * Consider this test case taken from portals.sql * * CREATE TABLE cursor (a int, b int) distribute by replication; * INSERT INTO cursor VALUES (10); * BEGIN; * SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; * DECLARE c1 NO SCROLL CURSOR FOR SELECT * FROM cursor FOR UPDATE; * INSERT INTO cursor VALUES (2); * FETCH ALL FROM c1; * would result in * ERROR: attempted to lock invisible tuple * because FETCH would be sent as a select to the remote nodes * with command id 0, whereas the command id would be 2 * in the current snapshot. * (1 sent by Coordinator due to declare cursor & * 2 because of the insert inside the transaction) * The command id should therefore be updated in the * current snapshot. */ if (IsConnFromCoord()) SnapshotSetCommandId(GetCurrentCommandId(false)); #endif return CurrentSnapshot; } CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData); return CurrentSnapshot; }