Re: autonomous transactions

On 8 September 2016 at 08:18, Tsunakawa, Takayuki
 wrote:
> From: pgsql-hackers-owner@postgresql.org
> [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Craig Ringer
>> Of course, if we could decrease the startup cost of a bgworker
>
>> For this use in autonomous tx's we could probably pool workers. Or at least
>> lazily terminate them so that the loop cases work better by re-using an
>> existing bgworker.
>
> I’m not sure whether to be nervous about the context switch cost in the use
> cases of autonomous transactions.

That's probably going to be one of the smaller costs. Doing this with
bgworkers won't be cheap, but you need to consider the alternative.
Factoring out all transaction-specific data currently stored in or
pointed to by globals into a transaction state struct that can be
swapped out. Making PgXact and PGPROC capable of representing
multiple/suspended transactions. Lots more. Much of which would have a
performance impact on all day to day operations whether or not
autononomous xacts are actually in use.

I haven't looked into it in detail. Peter can probably explain more
and better. I'm just pointing out that I doubt there's any way to do
this without a cost somewhere, and having that cost limited to actual
uses of autonomous xacts would be nice.

(BTW, could you please set your reply style so that your mail client
quotes text and it's possible to see what you wrote vs what is
quoted?)

-- 
-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services