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Understanding pg_xlog

From: shingav <shingav(at)gmail(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Understanding pg_xlog
Date: 2005-03-31 08:05:04
Message-ID: 3846dd305033100051a5ae6e3@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Hello,

I am trying to understand the way in which PostgreSQL creates, updates
and uses the transaction log.

I browsed through the sources and what I understand is that, when we
"initdb", the "initdb" binary reads postgres.bki which is created by
genbki.sh.

But I fail to understand how data is stored (written) in the
"000001xxxxx" file. I came across some CRC and compression code.

I used a hexeditor to deciphar the contents of "000001xxxx" file but
it was not of much help.

Are the query (inserts/updates) put as is in the transaction log file ?

Does the CRC and compression logic transform the query ?

While we do a recovery, does it backtrace these CRC and compression
logic to retrieve the query ?

Thanks,
Shinga

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