On 26/2/2025 13:14, Alexander Korotkov wrote:
On Mon, Feb 24, 2025 at 2:22 PM Andrei Lepikhov <lepi...@gmail.com> wrote:
On 24/2/2025 11:57, Alexander Korotkov wrote:
Could you, please, elaborate more on what you mean by "new technique
of query tree reduction"?
I mean any transformations and optimisations that reduce search space
for optimisation. Right now, I see the features reduce_unique_semijoins,
remove_useless_joins, and remove_useless_self_joins.
In practice, I see at least a join on a foreign key, where some cases
potentially allow the removal of the JOIN operator.
Do you mean some generic facility, which generalizes all the
transformations you mentioned? If so, it would be cool. But how
could it look like?
I think we may realise what it may look like by attempting to implement
more RelOptInfo-removal features. Right now, I have only vague ideas on
that subject. Just for reference, there were other discussions on join
removal [1 - 5] and some blog posts explaining Oracle techniques in this
area - see, for example, [6].
[1] inner join removal
https://www.postgresql.org/message-id/flat/AANLkTinS_MlZ2F3Siwgcje--qf5nTJTpuHFnZdcA45bU%40mail.gmail.com
[2] Patch to support SEMI and ANTI join removal
https://www.postgresql.org/message-id/flat/CAApHDvpCBEfuc5tD%3DvniepAv0pU5m%3Dq%3DfOQZcOdMHeei7OQPgQ%40mail.gmail.com
[3] Removing INNER JOINs
https://www.postgresql.org/message-id/flat/CAApHDvocUEYdt1uT+DLDPs2xEu=v3qjgt6hexkonqm4ry_o...@mail.gmail.com#CAApHDvocUEYdt1uT+DLDPs2xEu=v3qjgt6hexkonqm4ry_o...@mail.gmail.com
[4] WIP Join Removal
https://www.postgresql.org/message-id/flat/1220176372.4371.118.camel%40ebony.2ndQuadrant
[5] Join Removal/ Vertical Partitioning
https://www.postgresql.org/message-id/flat/1214477827.3845.87.camel%40ebony.site
[6] Oracle Join Elimination
https://oracle-base.com/articles/misc/join-elimination
--
regards, Andrei Lepikhov
