Re: Speed up Clog Access by increasing CLOG buffers

On Sat, Dec 12, 2015 at 8:03 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:

>> I think it might be
>> advantageous to have at least two groups because otherwise things
>> might slow down when some transactions are rolling over to a new page
>> while others are still in flight for the previous page. Perhaps we
>> should try it both ways and benchmark.
>>
>
> Sure, I can do the benchmarks with both the patches, but before that
> if you can once check whether group_slots_update_clog_v3.patch is inline
> with what you have in mind then it will be helpful.

Benchmarking sounds good. This looks broadly like what I was thinking
about, although I'm not very sure you've got all the details right.

Some random comments:

- TransactionGroupUpdateXidStatus could do just as well without
add_proc_to_group. You could just say if (group_no >= NUM_GROUPS)
break; instead. Also, I think you could combine the two if statements
inside the loop. if (nextidx != INVALID_PGPROCNO &&
ProcGlobal->allProcs[nextidx].clogPage == proc->clogPage) break; or
something like that.

- memberXid and memberXidstatus are terrible names. Member of what?
That's going to be clear as mud to the next person looking at the
definitiono f PGPROC. And the capitalization of memberXidstatus isn't
even consistent. Nor is nextupdateXidStatusElem. Please do give some
thought to the names you pick for variables and structure members.

--
Robert Haas
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