Re: Toast, Text, blob bytea Huh?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter T Mount <peter(at)retep(dot)org(dot)uk>
Cc: Joe Conway <joseph(dot)conway(at)home(dot)com>, jason(dot)ory(at)ndchealth(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Toast, Text, blob bytea Huh?
Date: 2001-08-24 15:15:07
Message-ID: 3241.998666107@sss.pgh.pa.us
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Peter T Mount <peter(at)retep(dot)org(dot)uk> writes:
> Quoting Joe Conway <joseph(dot)conway(at)home(dot)com>:
>> indicating that the practical limit is closer to 1 GB -- not sure why).

> It may be something to do with the 1Gb splitting of the physical files
> representing a table...

No, that's just a coincidence. The reason that TOAST limits fields to
1Gb is that the high-order two bits of the varlena length word were
commandeered as TOAST state indicators. There are now only thirty bits
available to represent the length of a variable-length Datum; hence the
hard limit on field width is 1Gb.

I'd think that the "practical" limit is quite a bit less than that, at
least until we devise an API that lets you read and write toasted values
in sections.

regards, tom lane

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