Re: [HACKERS] Open 6.5 items

Vadim Mikheev <vadim(at)krs(dot)ru> writes:
>> If I recall the dynahash.c code correctly, a null return value
>> indicates either damage to the structure of the table (ie someone
>> stomped on memory that didn't belong to them) or running out of memory
>> to add entries to the table. The latter should be impossible if we

> Quite different cases and should result in different reactions.

I agree; will see about cleaning up hash_search's call convention after
6.5 is done. Actually, maybe I should do it now? I'm not convinced yet
whether the reports we're seeing are due to memory clobber or running
out of space... fixing this may be the easiest way to find out.

> #define NLOCKS_PER_XACT 40
> ^^
> Isn't it too low?

You tell me ... that was the number that was in the 6.4 code, but I
have no idea if it's right or not. (Does MVCC require more locks
than the old stuff?) What is a good upper bound on the number
of concurrently existing locks?

> /* xidHash table */
> size += hash_estimate_size(maxBackends,
> ^^^^^^^^^^^
> SHMEM_XIDTAB_KEYSIZE,
> SHMEM_XIDTAB_DATASIZE);

> Why just maxBackends is here? NLOCKENTS should be used too
> (each transaction lock requieres own xidhash entry).

Should it be NLOCKENTS(maxBackends) xid entries, or do you mean
NLOCKENTS(maxBackends) + maxBackends? Feel free to stick in any
estimates that you like better --- what's there now is an interpretation
of what the 6.4 code was trying to do (but it was sufficiently buggy and
unreadable that it was probably coming out with different numbers in
the end...)

regards, tom lane