| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Markus Wanner <markus(at)bluegap(dot)ch>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Synchronous Log Shipping Replication |
| Date: | 2008-09-09 15:06:33 |
| Message-ID: | 1220972793.3913.514.camel@ebony.2ndQuadrant |
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| Lists: | pgsql-hackers |
On Tue, 2008-09-09 at 17:17 +0300, Heikki Linnakangas wrote:
> Tom Lane wrote:
> > Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> >> On Tue, 2008-09-09 at 08:24 -0400, Tom Lane wrote:
> >>> "Agreed"? That last restriction is a deal-breaker.
> >
> >> OK, I should have said *if wal_buffers are full* XLogInsert() cannot
> >> advance to a new page while we are waiting to send or write. So I don't
> >> think its a deal breaker.
> >
> > Oh, OK, that's obvious --- there's no place to put more data.
>
> Each WAL sender can keep at most one page locked at a time, right? So,
> that should never happen if wal_buffers > 1 + n_wal_senders.
Don't understand. I am referring to the logic at the top of
AdvanceXLInsertBuffer(). We would need to wait for all people reading
the contents of wal_buffers.
Currently, there is no page locking on the WAL buffers, though I have
suggested some for increasing XLogInsert() performance.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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