From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
Cc: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: "caught_up" status in walsender |
Date: | 2010-06-03 15:26:07 |
Message-ID: | 26798.1275578767@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
I wrote:
> On further contemplation, it seems like the protocol needs another field
> besides that: each record should also carry a boolean indicating whether
> walsender.c thinks it is currently "caught up", ie the record carries
> all WAL data up to the current end of WAL.
Actually, there's a better way to do that: let's have the record carry
not just a boolean but the actual current end-of-WAL LSN. The receiver
could then not just determine "am I behind" but find out *how far*
behind it is, and thereby perhaps adjust its behavior in more subtle
ways than just a binary on/off fashion.
(Actually doing anything like that is material for future work, of
course, but I think we should try to get the SR protocol right now.)
regards, tom lane
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