From: | Florian Pflug <fgp(at)phlo(dot)org> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <gsstark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: beta3 & the open items list |
Date: | 2010-06-19 23:11:44 |
Message-ID: | 98BC0D4B-731B-4D63-970E-145A77B236D9@phlo.org |
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Lists: | pgsql-hackers |
On Jun 19, 2010, at 21:13 , Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Right now, if the SR master reboots unexpectedly (say, power plug pull
>> and restart), the slave never notices. It just sits there forever
>> waiting for the next byte of data from the master to arrive (which it
>> never will).
>
> This is nonsense --- the slave's kernel *will* eventually notice that
> the TCP connection is dead, and tell walreceiver so. I don't doubt
> that the standard TCP timeout is longer than people want to wait for
> that, but claiming that it will never happen is simply wrong.
No, Robert is correct AFAIK. If you're *waiting* for data, TCP generates no traffic (expect with keepalive enabled). From the slave's kernel POV, a dead master is therefore indistinguishable from a inactive master.
Things are different from a sender's POV, though. Since sent data is ACK'ed by the receiving end, the TCP stack can (and does) detect a broken connection.
best regards,
Florian Pflug
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