Re: SSI bug?

On 31.03.2011 22:06, Kevin Grittner wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>
>> That's not enough. The hash tables can grow beyond the maximum
>> size you specify in ShmemInitHash. It's just a hint to size the
>> directory within the hash table.
>>
>> We'll need to teach dynahash not to allocate any more entries
>> after the preallocation. A new HASH_NO_GROW flag to hash_create()
>> seems like a suitable interface.
>
> OK. If we're doing that, is it worth taking a look at the "safety
> margin" added to the size calculations, and try to make the
> calculations more accurate?
>
> Would you like me to code a patch for this?

I finally got around to look at this. Attached patch adds a
HASH_FIXED_SIZE flag, which disables the allocation of new entries after
the initial allocation. I believe we have consensus to make the
predicate lock hash tables fixed-size, so that there's no competition of
the slack shmem space between predicate lock structures and the regular
lock maanager.

I also noticed that there's a few hash_search(HASH_ENTER) calls in
predicate.c followed by check for a NULL result. But with HASH_ENTER,
hash_search never returns NULL, it throws an "out of shared memory"
error internally. I changed those calls to use HASH_ENTER_NULL, so you
now get the intended error message with the hint to raise
max_pred_locks_per_transaction.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com