Re: Table AM modifications to accept column projection lists - Mailing list pgsql-hackers

On Mon, Sep 05, 2022 at 05:38:51PM +0300, Nikita Malakhov wrote:
> Due to experiments with columnar data storage I've decided to revive this
> thread - Table AM modifications to accept column projection lists
> <https://www.postgresql.org/message-id/flat/CAE-ML+9RmTNzKCNTZPQf8O3b-UjHWGFbSoXpQa3Wvuc8YBbEQw@mail.gmail.com>
>
> To remind:
>
> This patch introduces a set of changes to the table AM APIs, making them
> accept a column projection list. That helps columnar table AMs, so that
> they don't need to fetch all columns from disk, but only the ones
> actually needed.
>
> The set of changes in this patch is not exhaustive -
> there are many more opportunities that are discussed in the TODO section
> below. Before digging deeper, we want to elicit early feedback on the
> API changes and the column extraction logic.
>
> TableAM APIs that have been modified are:
>
> 1. Sequential scan APIs
> 2. Index scan APIs
> 3. API to lock and return a row
> 4. API to fetch a single row
>
> We have seen performance benefits in Zedstore for many of the optimized
> operations [0]. This patch is extracted from the larger patch shared in
> [0].

What parts of the original patch were left out ?  This seems to be the
same size as the original.

With some special build options like -DWRITE_READ_PARSE_PLAN_TREES, this
currently fails with:

WARNING:  outfuncs/readfuncs failed to produce equal parse tree

There's poor code coverage in PopulateNeededColumnsForScan()
IndexNext(), check_default_partition_contents() and nodeSeqscan.c.
https://cirrus-ci.com/task/5516554904272896
https://api.cirrus-ci.com/v1/artifact/task/5516554904272896/coverage/coverage/00-index.html

Is it currently possible to hit those code paths in postgres ?  If not,
you may need to invent a minimal columnar extension to allow excercising
that.

Note that the cirrusci link is on top of my branch which runs "extended"
checks in cirrusci, but you can also run code coverage report locally
with --enable-coverage.

When you mail next, please run pgindent first (BTW there's a debian
package in PGDG for pgindent).

--
Justin