Re: Table and Index compression

From: Pierre Frédéric Caillaud <lists(at)peufeu(dot)com>
To: "Greg Stark" <gsstark(at)mit(dot)edu>, "Sam Mason" <sam(at)samason(dot)me(dot)uk>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Table and Index compression
Date: 2009-08-07 11:06:10
Message-ID: op.uyag4kzicke6l8@soyouz
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> Also, I'm puzzled why it would the space increase would proportional
> to the amount of data and be more than 300 bytes. There's no reason it
> wouldn't be a small fixed amount. The ideal is you set aside one bit
> -- if the bit is set the rest is compressed and has to save at least
> one bit. If the bit is not set then the rest is uncompressed. Maximum
> bloat is 1-bit. In real systems it's more likely to be a byte or a
> word.

I'm working on cleaning the patch...

I added a field in PageHeader which contains :
- 0 to indicate a non-compressed page
- length of compressed data if compressed

If compression gains nothing (ie gains less than 4K), the page is stored
raw.

It seems that only pages having a PageHeader are handled by md.c, so it
should work (am I mistaken ?)

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