| From: | Hannu Krosing <hannu(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: cheaper snapshots |
| Date: | 2011-07-28 16:48:24 |
| Message-ID: | 1311871704.3117.1577.camel@hvost |
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| Lists: | pgsql-hackers |
On Thu, 2011-07-28 at 18:05 +0200, Hannu Krosing wrote:
> But it is also possible, that you can get logically consistent snapshots
> by protecting only some ops. for example, if you protect only insert and
> get snapshot, then the worst that can happen is that you get a snapshot
> that is a few commits older than what youd get with full locking and it
> may well be ok for all real uses.
Thinking more of it, we should lock commit/remove_txid and get_snapshot
having a few more running backends does not make a difference, but
seeing commits in wrong order may.
this will cause contention between commit and get_snapshot, but
hopefully less than current ProcArray manipulation, as there is just one
simple C array to lock and copy.
--
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Hannu Krosing
PostgreSQL Infinite Scalability and Performance Consultant
PG Admin Book: http://www.2ndQuadrant.com/books/
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