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Commitdc02b98

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At update of non-LP_NORMAL TID, fail instead of corrupting page header.
The right mix of DDL and VACUUM could corrupt a catalog page header suchthat PageIsVerified() durably fails, requiring a restore from backup.This affects only catalogs that both have a syscache and have DDL codethat uses syscache tuples to construct updates. One of the testpermutations shows a variant not yet fixed.This makes !TransactionIdIsValid(TM_FailureData.xmax) possible withTM_Deleted. I think core and PGXN are indifferent to that.Per bug #17821 from Alexander Lakhin. Back-patch to v13 (all supportedversions). The test case is v17+, since it uses INJECTION_POINT.Discussion:https://postgr.es/m/17821-dd8c334263399284@postgresql.org
1 parent216294b commitdc02b98

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+46
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lines changed

2 files changed

+46
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lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 44 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -72,6 +72,7 @@
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#include"utils/relcache.h"
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#include"utils/snapmgr.h"
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#include"utils/spccache.h"
75+
#include"utils/syscache.h"
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staticHeapTupleheap_prepare_insert(Relationrelation,HeapTupletup,
@@ -3242,7 +3243,49 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
32423243
LockBuffer(buffer,BUFFER_LOCK_EXCLUSIVE);
32433244

32443245
lp=PageGetItemId(page,ItemPointerGetOffsetNumber(otid));
3245-
Assert(ItemIdIsNormal(lp));
3246+
3247+
/*
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* Usually, a buffer pin and/or snapshot blocks pruning of otid, ensuring
3249+
* we see LP_NORMAL here. When the otid origin is a syscache, we may have
3250+
* neither a pin nor a snapshot. Hence, we may see other LP_ states, each
3251+
* of which indicates concurrent pruning.
3252+
*
3253+
* Failing with TM_Updated would be most accurate. However, unlike other
3254+
* TM_Updated scenarios, we don't know the successor ctid in LP_UNUSED and
3255+
* LP_DEAD cases. While the distinction between TM_Updated and TM_Deleted
3256+
* does matter to SQL statements UPDATE and MERGE, those SQL statements
3257+
* hold a snapshot that ensures LP_NORMAL. Hence, the choice between
3258+
* TM_Updated and TM_Deleted affects only the wording of error messages.
3259+
* Settle on TM_Deleted, for two reasons. First, it avoids complicating
3260+
* the specification of when tmfd->ctid is valid. Second, it creates
3261+
* error log evidence that we took this branch.
3262+
*
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* Since it's possible to see LP_UNUSED at otid, it's also possible to see
3264+
* LP_NORMAL for a tuple that replaced LP_UNUSED. If it's a tuple for an
3265+
* unrelated row, we'll fail with "duplicate key value violates unique".
3266+
* XXX if otid is the live, newer version of the newtup row, we'll discard
3267+
* changes originating in versions of this catalog row after the version
3268+
* the caller got from syscache. See syscache-update-pruned.spec.
3269+
*/
3270+
if (!ItemIdIsNormal(lp))
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{
3272+
Assert(RelationSupportsSysCache(RelationGetRelid(relation)));
3273+
3274+
UnlockReleaseBuffer(buffer);
3275+
Assert(!have_tuple_lock);
3276+
if (vmbuffer!=InvalidBuffer)
3277+
ReleaseBuffer(vmbuffer);
3278+
tmfd->ctid=*otid;
3279+
tmfd->xmax=InvalidTransactionId;
3280+
tmfd->cmax=InvalidCommandId;
3281+
3282+
bms_free(hot_attrs);
3283+
bms_free(key_attrs);
3284+
bms_free(id_attrs);
3285+
/* modified_attrs not yet initialized */
3286+
bms_free(interesting_attrs);
3287+
returnTM_Deleted;
3288+
}
32463289

32473290
/*
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* Fill in enough data in oldtup for HeapDetermineColumnsInfo to work

‎src/include/access/tableam.h

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -113,7 +113,8 @@ typedef enum TM_Result
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*
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* xmax is the outdating transaction's XID. If the caller wants to visit the
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* replacement tuple, it must check that this matches before believing the
116-
* replacement is really a match.
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* replacement is really a match. This is InvalidTransactionId if the target
117+
* was !LP_NORMAL (expected only for a TID retrieved from syscache).
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*
118119
* cmax is the outdating command's CID, but only when the failure code is
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* TM_SelfModified (i.e., something in the current transaction outdated the

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