Message-ID: <141202ca-4c92-e294-0bfe-e1709ee2f71b@enterprisedb.com>
Date: Sun, 7 May 2023 00:13:07 +0200
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Subject: Re: Missing update of all_hasnulls in BRIN opclasses
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
 Matthias van de Meent <boekewurm+postgres@gmail.com>,
 pgsql-hackers@lists.postgresql.org
References: <20230424153648.cyaifmcchslbcsrf@alvherre.pgsql>
 <491ba86b-6294-37bb-fe00-c91e829dfc82@enterprisedb.com>
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On 4/24/23 23:20, Tomas Vondra wrote:
> On 4/24/23 17:36, Alvaro Herrera wrote:
>> On 2023-Apr-23, Tomas Vondra wrote:
>>
>>> here's an updated version of the patch, including a backport version. I
>>> ended up making the code yet a bit closer to master by introducing
>>> add_values_to_range(). The current pre-14 code has the loop adding data
>>> to the BRIN tuple in two places, but with the "fixed" logic handling
>>> NULLs and the empty_range flag the amount of duplicated code got too
>>> high, so this seem reasonable.
>>
>> In backbranches, the new field to BrinMemTuple needs to be at the end of
>> the struct, to avoid ABI breakage.
>>

Unfortunately, this is not actually possible :-(

The BrinMemTuple has a FLEXIBLE_ARRAY_MEMBER at the end, so we can't
place anything after it. I think we have three options:

a) some other approach? - I really can't see any, except maybe for going
back to the previous approach (i.e. encoding the info using the existing
BrinValues allnulls/hasnulls flags)

b) encoding the info in existing BrinMemTuple flags - e.g. we could use
bt_placeholder to store two bits, not just one. Seems a bit ugly.

c) ignore the issue - AFAICS this would be an issue only for (external)
code accessing BrinMemTuple structs, but I don't think we're aware of
any out-of-core BRIN opclasses or anything like that ...


regards

-- 
Tomas Vondra
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