Re: Exposing the Xact commit order to the user

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Jan Wieck <JanWieck(at)yahoo(dot)com>
Cc: PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Exposing the Xact commit order to the user
Date: 2010-05-26 14:04:21
Message-ID: AANLkTinqlFtvpS-45F354qVSBJ49MHjBRG1ucMc75HZo@mail.gmail.com
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On Sun, May 23, 2010 at 9:21 PM, Jan Wieck <JanWieck(at)yahoo(dot)com> wrote:
> Each record of the Transaction Commit Info consists of
>
>     txid          xci_transaction_id
>     timestamptz   xci_begin_timestamp
>     timestamptz   xci_commit_timestamp
>     int64         xci_total_rowcount
>

So I think you're going about this backwards.

Instead of discussing implementation I think you should start with the
API the replication system needs. In particular I'm not sure you
really want a server-side query at all. I'm wondering if you wouldn't
be better off with a public machine-parsable text format version of
the WAL. Ie, at the same time as writing out all the nitty gritty to
the binary wal we would write out a summary of public data to an xml
version containing just parts of the data stream that we can promise
won't change, such as transaction id, lsn, timestamp.

--
greg

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