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Commit073afae

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author
Amit Kapila
committed
Avoid possible deadlock while locking multiple heap pages.
To avoid deadlock, backend acquires a lock on heap pages in blocknumber order. In certain cases, lock on heap pages is dropped andreacquired. In this case, the locks are dropped for reading incorresponding VM page/s. The issue is we re-acquire locks in bufferIdorder whereas the intention was to acquire in blockid order.This commit ensures that we will always acquire locks on heap pages inblockid order.Reported-by: Nishant FnuAuthor: Nishant FnuReviewed-by: Amit Kapila and Robert HaasBackpatch-through: 9.4Discussion:https://postgr.es/m/5883C831-2ED1-47C8-BFAC-2D5BAE5A8CAE@amazon.com
1 parent014763e commit073afae

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lines changed
  • src/backend/access/heap

1 file changed

+4
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‎src/backend/access/heap/hio.c‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -115,8 +115,8 @@ ReadBufferBI(Relation relation, BlockNumber targetBlock,
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* visibility map page, if we haven't already got one.
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*
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* buffer2 may be InvalidBuffer, if only one buffer is involved. buffer1
118-
* must not be InvalidBuffer. If both buffers are specified,buffer1 must
119-
* be less thanbuffer2.
118+
* must not be InvalidBuffer. If both buffers are specified,block1 must
119+
* be less thanblock2.
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*/
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staticvoid
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GetVisibilityMapPins(Relationrelation,Bufferbuffer1,Bufferbuffer2,
@@ -127,7 +127,7 @@ GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
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boolneed_to_pin_buffer2;
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Assert(BufferIsValid(buffer1));
130-
Assert(buffer2==InvalidBuffer||buffer1 <=buffer2);
130+
Assert(buffer2==InvalidBuffer||block1 <=block2);
131131

132132
while (1)
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{
@@ -449,7 +449,7 @@ RelationGetBufferForTuple(Relation relation, Size len,
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* done a bit of extra work for no gain, but there's no real harm
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* done.
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*/
452-
if (otherBuffer==InvalidBuffer||buffer <=otherBuffer)
452+
if (otherBuffer==InvalidBuffer||targetBlock <=otherBlock)
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GetVisibilityMapPins(relation,buffer,otherBuffer,
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targetBlock,otherBlock,vmbuffer,
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vmbuffer_other);

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