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Commit2168f37

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Ignore CatalogSnapshot when checking COPY FREEZE prerequisites.
This restores the ability, essentially lost in commitffaa44c, to use COPY FREEZE underREPEATABLE READ isolation. Back-patch to 9.4, like that commit.Reviewed by Tom Lane.Discussion:https://postgr.es/m/CA+TgmoahWDm-7fperBxzU9uZ99LPMUmEpSXLTw9TmrOgzwnORw@mail.gmail.com
1 parentc3f43a7 commit2168f37

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2 files changed

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2 files changed

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‎src/backend/commands/copy.c‎

Lines changed: 15 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2392,13 +2392,25 @@ CopyFrom(CopyState cstate)
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/*
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* Optimize if new relfilenode was created in this subxact or one of its
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* committed children and we won't see those rows later as part of an
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* earlier scan or command.Thisensures that if thissubtransaction
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* aborts then the frozen rows won't be visible after xact cleanup. Note
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* earlier scan or command.The subxact testensures that if thissubxact
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* aborts then the frozen rows won't be visible after xact cleanup.Note
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* that the stronger test of exactly which subtransaction created it is
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* crucial for correctness of this optimization.
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* crucial for correctness of this optimization. The test for an earlier
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* scan or command tolerates false negatives. FREEZE causes other sessions
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* to see rows they would not see under MVCC, and a false negative merely
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* spreads that anomaly to the current session.
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*/
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if (cstate->freeze)
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{
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/*
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* Tolerate one registration for the benefit of FirstXactSnapshot.
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* Scan-bearing queries generally create at least two registrations,
2408+
* though relying on that is fragile, as is ignoring ActiveSnapshot.
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* Clear CatalogSnapshot to avoid counting its registration. We'll
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* still detect ongoing catalog scans, each of which separately
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* registers the snapshot it uses.
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*/
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InvalidateCatalogSnapshot();
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if (!ThereAreNoPriorRegisteredSnapshots()|| !ThereAreNoReadyPortals())
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_TRANSACTION_STATE),

‎src/backend/utils/time/snapmgr.c‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1645,6 +1645,14 @@ DeleteAllExportedSnapshotFiles(void)
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FreeDir(s_dir);
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}
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/*
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* ThereAreNoPriorRegisteredSnapshots
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*Is the registered snapshot count less than or equal to one?
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*
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* Don't use this to settle important decisions. While zero registrations and
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* no ActiveSnapshot would confirm a certain idleness, the system makes no
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* guarantees about the significance of one registered snapshot.
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*/
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bool
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ThereAreNoPriorRegisteredSnapshots(void)
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{

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