On 14.01.2011 14:18, Simon Riggs wrote:
On Fri, 2011-01-14 at 14:08 +0200, Heikki Linnakangas wrote:
On 14.01.2011 14:01, Simon Riggs wrote:
On Fri, 2011-01-14 at 13:47 +0200, Heikki Linnakangas wrote:
On 14.01.2011 13:15, Simon Riggs wrote:
/*
+ * Recheck shared recoveryPause by polling.
+ *
+ * XXX It might seem we should do this via a shared Latch, but
+ * currently we only support one shared latch per process and
+ * that is already taken for Startup process. Polling is used
+ * in other places in xlog.c already, so not a concern.
+ */
There is no such limitation with latches.
SIGUSR1 handler can only handle one shared latch
You can only *wait* for one latch at a time, but you can own more than
that. AFAICS you would never need to wait for the recovery-pause-latch
at the same time as the other latch.
Yes, I understand.
Trouble is, if you wait on Latch X and other processes send wakeup
assuming you were waiting on Latch Y, then this will erroneously wake
you up.
The signal will wake up the process, but WaitLatch will quickly go back
to sleep if it wasn't for the latch we're waiting for. I don't think
that causes any meaningful performance issues.
So that's all handled within the latch code.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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