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hio: Relax rules for calling GetVisibilityMapPins() 

GetVisibilityMapPins() insisted on the buffer1/buffer2 being in a specific
order. This required checks at the callsite. As a subsequent patch will add
another callsite, move related logic into GetVisibilityMapPins().

Discussion: https://postgr.es/m/20230403190030.fk2frxv6faklrseb@awork3.anarazel.de
This commit is contained in:
Andres Freund 2023-04-06 10:27:30 -07:00
parent 00beecfe83
commit bba9003b62
1 changed files with 26 additions and 11 deletions
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37
src/backend/access/heap/hio.c
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@ -131,9 +131,9 @@ ReadBufferBI(Relation relation, BlockNumber targetBlock,
* For each heap page which is all-visible, acquire a pin on the appropriate
* visibility map page, if we haven't already got one.
*
* buffer2 may be InvalidBuffer, if only one buffer is involved. buffer1
* must not be InvalidBuffer. If both buffers are specified, block1 must
* be less than block2.
* To avoid complexity in the callers, either buffer1 or buffer2 may be
* InvalidBuffer if only one buffer is involved. For the same reason, block2
* may be smaller than block1.
*/
static void
GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
@ -143,6 +143,26 @@ GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2,
bool need_to_pin_buffer1;
bool need_to_pin_buffer2;
/*
* Swap buffers around to handle case of a single block/buffer, and to
* handle if lock ordering rules require to lock block2 first.
*/
if (!BufferIsValid(buffer1) ||
(BufferIsValid(buffer2) && block1 > block2))
{
Buffer tmpbuf = buffer1;
Buffer *tmpvmbuf = vmbuffer1;
BlockNumber tmpblock = block1;
buffer1 = buffer2;
vmbuffer1 = vmbuffer2;
block1 = block2;
buffer2 = tmpbuf;
vmbuffer2 = tmpvmbuf;
block2 = tmpblock;
}
Assert(BufferIsValid(buffer1));
Assert(buffer2 == InvalidBuffer || block1 <= block2);
@ -502,14 +522,9 @@ loop:
* done a bit of extra work for no gain, but there's no real harm
* done.
*/
if (otherBuffer == InvalidBuffer || targetBlock <= otherBlock)
GetVisibilityMapPins(relation, buffer, otherBuffer,
targetBlock, otherBlock, vmbuffer,
vmbuffer_other);
else
GetVisibilityMapPins(relation, otherBuffer, buffer,
otherBlock, targetBlock, vmbuffer_other,
vmbuffer);
GetVisibilityMapPins(relation, buffer, otherBuffer,
targetBlock, otherBlock, vmbuffer,
vmbuffer_other);
/*
* Now we can check to see if there's enough free space here. If so,