Re: SSI freezing bug

Andres Freund <andres@2ndquadrant.com> wrote:
> On 2013-10-01 07:41:46 -0700, Kevin Grittner wrote:
>> Andres Freund <andres@2ndquadrant.com> wrote:
>>
>>> A better solution probably is to promote tuple-level locks if
>>> they exist to a relation level one upon freezing I guess?
>>
>> It would be sufficient to promote the tuple lock to a page lock.
>> It would be pretty easy to add a function to predicate.c which
>> would accept a Relation and HeapTuple, check for a predicate lock
>> for the tuple, and add a page lock if found (which will
>> automatically clear the tuple lock).  This new function would be
>> called when a tuple was chosen for freezing.  Since freezing always
>> causes WAL-logging and disk I/O, the cost of a couple hash table
>> operations should not be noticeable.
>
> Yea, not sure why I was thinking of table level locks.
>
>> This seems like a bug fix which should be back-patched to 9.1, yes?
>
> Yes.

Patch attached, including new isolation test based on Heikki's
example.  This patch does change the signature of
heap_freeze_tuple().  If anyone thinks there is risk that external
code may be calling this, I could keep the old function with its
old behavior (including the bug) and add a new function name with
the new parameters added -- the old function could call the new one
with NULL for the last two parameters.  I'm not sure whether that
is better than breaking a compile of code which uses the old
signature, which would force a choice about what to do.

Will give it a couple days for feedback before pushing.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company