Re: Group Commit

Heikki Linnakangas wrote:
> Here's what's happening:
> 
> 1. Client 1 issues fsync (A)
> 2. Clients 2-5 write their commit record, and try to fsync, but they 
> have to wait for fsync (A) to finish.

> It contains a graph that shows that the patch works very well for this 
> test case. It's not very good for real life as it is, though. An obvious 
> flaw is that if you have a longer-running transaction, effect 1. goes 
> away. Instead of waiting for NBackends commit records, we should try to 
> guess the number of transactions that are likely to finish in a 
> reasonably short time. I'm thinking of keeping a running average of 
> commits per second, or # of transactions that finish while an fsync is 
> taking place.
> 
> Any thoughts?

Well, you did say *any* thoughts, so I guess mine count :-)

Do you not want to minimise the cost of #2 in your sequence? Some 
measure of "total backend time spent waiting to commit".

I don't know how simple it is to measure/estimate the time spent for "# 
of transactions that finish while an fsync is  taking place".

--   Richard Huxton  Archonet Ltd