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Commitf99870d

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Fix corruption of toast indexes with REINDEX CONCURRENTLY
REINDEX CONCURRENTLY run on a toast index or a toast relation couldcorrupt the target indexes rebuilt, as a backend running in parallelthat manipulates toast values would directly release the lock on thetoast relation when its local operation is done, rather than releasingthe lock once the transaction that manipulated the toast valuescommitted.The fix done here is simple: we now hold a ROW EXCLUSIVE lock on thetoast relation when saving or deleting a toast value until thetransaction working on them is committed, so as a concurrent reindexhappening in parallel would be able to wait for any activity and see anynew rows inserted (or deleted).An isolation test is added to check after the case fixed here, which isa bit fancy by design as it relies on allow_system_table_mods to renamethe toast table and its index to fixed names. This way, it is possibleto reindex them directly without any dependency on the OID of theunderlying relation. Note that this could not use a DO block either, asREINDEX CONCURRENTLY cannot be run in a transaction block. The test isbackpatched down to 13, where it is possible, thanks toc4a7a39, to useallow_system_table_mods in a test suite.Reported-by: Alexey ErmakovAnalyzed-by: Andres Freund, Noah MischAuthor: Michael PaquierReviewed-by: Nathan BossartDiscussion:https://postgr.es/m/17268-d2fb426e0895abd4@postgresql.orgBackpatch-through: 12
1 parentedc2332 commitf99870d

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‎src/backend/access/common/toast_internals.c

Lines changed: 10 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -359,10 +359,12 @@ toast_save_datum(Relation rel, Datum value,
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}
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/*
362-
* Done - close toast relation and its indexes
362+
* Done - close toast relation and its indexes but keep the lock until
363+
* commit, so as a concurrent reindex done directly on the toast relation
364+
* would be able to wait for this transaction.
363365
*/
364-
toast_close_indexes(toastidxs,num_indexes,RowExclusiveLock);
365-
table_close(toastrel,RowExclusiveLock);
366+
toast_close_indexes(toastidxs,num_indexes,NoLock);
367+
table_close(toastrel,NoLock);
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/*
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* Create the TOAST pointer value that we'll return
@@ -439,11 +441,13 @@ toast_delete_datum(Relation rel, Datum value, bool is_speculative)
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}
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441443
/*
442-
* End scan and close relations
444+
* End scan and close relations but keep the lock until commit, so as a
445+
* concurrent reindex done directly on the toast relation would be able to
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* wait for this transaction.
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*/
444448
systable_endscan_ordered(toastscan);
445-
toast_close_indexes(toastidxs,num_indexes,RowExclusiveLock);
446-
table_close(toastrel,RowExclusiveLock);
449+
toast_close_indexes(toastidxs,num_indexes,NoLock);
450+
table_close(toastrel,NoLock);
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}
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/* ----------

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