Re: [HACKERS] MAIN, Uncompressed?

On 25 August 2017 at 14:08, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
>> On 25 August 2017 at 13:21, Tom Lane <tgl@sss.pgh.pa.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.

JSON blobs between 2kB and 8160 bytes are very common.

String length is maybe a poisson distribution, definitely not uniform.

-- 
Simon Riggs                http://www.2ndQuadrant.com/
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