Re: tracking commit timestamps

On 11/11/14, 2:03 PM, Alvaro Herrera wrote:
> Jim Nasby wrote:
>> On 11/10/14, 7:40 AM, Alvaro Herrera wrote:
>
>>> Ah, right. So AFAIK we don't need to keep anything older than
>>> RecentXmin or something like that -- which is not too old. If I recall
>>> correctly Josh Berkus was saying in a thread about pg_multixact that it
>>> used about 128kB or so in <= 9.2 for his customers; that one was also
>>> limited to RecentXmin AFAIR. I think a similar volume of commit_ts data
>>> would be pretty acceptable. Moreso considering that it's turned off by
>>> default.
>>
>> FWIW, AFAICS MultiXacts are only truncated after a (auto)vacuum process is able to advance datminmxid, which will (now) only happen when an entire relation has been scanned (which should be infrequent).
>>
>> I believe the low normal space usage is just an indication that most databases don't use many MultiXacts.
>
> That's in 9.3. Prior to that, they were truncated much more often.

Well, we're talking about a new feature, so I wasn't looking in back branches. ;P

> Maybe you've not heard enough about this commit:
>
> commit 0ac5ad5134f2769ccbaefec73844f8504c4d6182

Interestingly, git.postgresql.org hasn't either: http://git.postgresql.org/gitweb/?p=postgresql.git&a=search&h=HEAD&st=commit&s=0ac5ad5134f2769ccbaefec73844f8504c4d6182

The commit is certainly there though...
decibel(at)decina:[15:12]~/pgsql/HEAD/src/backend (master=)$git log 0ac5ad5134f2769ccbaefec73844f8504c4d6182|head -n1
commit 0ac5ad5134f2769ccbaefec73844f8504c4d6182
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com