| From: | "Lawrence, Ramon" <ramon(dot)lawrence(at)ubc(dot)ca> |
|---|---|
| To: | "Robert Haas" <robertmhaas(at)gmail(dot)com> |
| Cc: | <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: join removal |
| Date: | 2009-08-10 15:30:44 |
| Message-ID: | 6EEA43D22289484890D119821101B1DF05191043@exchange20.mercury.ad.ubc.ca |
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| Lists: | pgsql-hackers |
> I took at a first crack at coding up an implementation of
> relation_is_distinct_for() tonight.
I am not sure if this will help or not, but on the 8.4 code base we
implemented two functions:
- getCandidateKeys() - would recursively traverse a tree from a given
node to the leaf nodes and determine the candidate keys for the
intermediate relation produced by that node
- getJoinCard() - determined the join cardinality of a hash join node
(1:1, 1:N, etc.) based on the candidate keys of the two input relations
It worked pretty well for our tests with equi-joins, but I am sure it is
missing many cases. I have attached the code which we used
(cardinalityFuncs.c). Some of the helper functions may also be useful
(convertUniqueIndexesToCandidateKeys, getJoinAttrs).
--
Ramon Lawrence
| Attachment | Content-Type | Size |
|---|---|---|
| cardinalityFuncs.c | application/octet-stream | 15.9 KB |
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