From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: MAIN, Uncompressed? |
Date: | 2017-08-25 13:08:19 |
Message-ID: | 14901.1503666499@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> On 25 August 2017 at 13:21, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> If you know compression isn't useful, but you don't want to fail on
>> wide values, then "external" should serve the purpose.
> Well, almost. External toasts at 2048-ish bytes whereas Main toasts at
> 8160 bytes.
> The rows are typically near 4kB long, so if marked External they would
> always be toasted.
> It's desirable to have the full row in the heap block, rather than
> have to access heap-toastindex-toastblocks in all cases.
> The data is also incompressible, so Main just wastes time on insert.
> Hence, we have a missing option.
Maybe, but the use case seems mighty narrow.
regards, tom lane
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