16.09.2015 07:30, Jeff Janes:
The commit of this patch seems to have created a bug in which updated
tuples can disappear from the index, while remaining in the table.
It looks like the bug depends on going through a crash-recovery cycle,
but I am not sure of that yet.
I've looked through the commit diff and don't see anything obviously
wrong. I notice index tuples are marked dead with only a buffer
content share lock, and the page is defragmented with only a buffer
exclusive lock (as opposed to a super-exclusive buffer clean up
lock). But as far as I can tell, both of those should be safe on an
index. Also, if that was the bug, it should happen without
The test is pretty simple. I create a 10,000 row table with a
unique-by-construction id column with a btree_gist index on it and a
counter column, and fire single-row updates of the counter for random
ids in high concurrency (8 processes running flat out). I force the
server to crash frequently with simulated torn-page writes in which
md.c writes a partial page and then PANICs. Eventually (1 to 3 hours)
the updates start indicating they updated 0 rows. At that point, a
forced table scan will find the row, but the index doesn't.
Any hints on how to proceed with debugging this? If I can't get it to
reproduce the problem in the absence of crash-recovery cycles with an
overnight run, then I think my next step will be to run it over
hot-standby and see if WAL replay in the absence of crashes might be
broken as well.
I've found the bug. It's because of mixed calls of
PageIndexMultiDelete() in gistvacuumpage() and
PageIndexTupleDelete() in gistRedoPageUpdateRecord().
These functions are conflicting.
I've fixed my patch by change MultiDelete to TupleDelete in
gistvacuumpage(). Patch is attached.
But It seems to me that it would be better to rewrite all mentions of
TupleDelete to MultiDelete in gist code.
I'm working on it.
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diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 4edc5a7..1d02e1b 100644
@@ -1478,14 +1478,20 @@ gistvacuumpage(Relation rel, Page page, Buffer buffer)
ItemId itemId = PageGetItemId(page, offnum);
- deletable[ndeletable++] = offnum;
+ deletable[ndeletable] = offnum - ndeletable;
if (ndeletable > 0)
+ int i;
- PageIndexMultiDelete(page, deletable, ndeletable);
+ for (i = 0; i < ndeletable; i++)
+ PageIndexTupleDelete(page, deletable[i]);
* Mark the page as not containing any LP_DEAD items. This is not
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