Re: CURRENT OF causes an error when IndexOnlyScan is used

From: Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: CURRENT OF causes an error when IndexOnlyScan is used
Date: 2018-02-19 14:36:55
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01.02.2018 05:12, Tom Lane:
> Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp> writes:
>> I'm sorry the patch attached in the previous mail is broken and
>> not raises a compile error. I attached the fixed patch.
> This patch is almost certainly wrong: you can't assume that the scan-level
> state matches the tuple we are currently processing at top level. Any
> sort of delaying action, for instance a sort or materialize node in
> between, would break it.
> We need to either fix this aspect:
>>> IndexOnlyScan returns a virtual tuple that doesn't have system
>>> column, so we can not get ctid in the same way of other plans.

I'd like to propose the patch that fixes the issue.
We already have a way to return heaptuple from IndexOnlyScan,
but it was not applied to b-tree for some reason.

Attached patch solves the reported bug.
Moreover, it will come in handy for "index with included attributes"
feature [1],
where we can store long (and even TOASTed) attributes in indextuple.


Anastasia Lubennikova
Postgres Professional:
The Russian Postgres Company

Attachment Content-Type Size
return_heaptuple_in_btree_indexonlyscan_v1.patch text/x-patch 4.9 KB

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