Re: BUG #8576: 'btree index keys must be ordered by attribute' - Mailing list pgsql-bugs
From | Tom Lane |
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Subject | Re: BUG #8576: 'btree index keys must be ordered by attribute' |
Date | |
Msg-id | 17519.1383431162@sss.pgh.pa.us Whole thread Raw |
In response to | BUG #8576: 'btree index keys must be ordered by attribute' (peter.hicks@poggs.co.uk) |
Responses |
Re: BUG #8576: 'btree index keys must be ordered by attribute'
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List | pgsql-bugs |
peter.hicks@poggs.co.uk writes: > The SQL code further down allows a btree index to be created with the same > column twice, however no queries are possible on the table and are met with > a "ERROR: XX000: btree index keys must be ordered by attribute". > It looks like bug #6351 > (http://www.postgresql.org/message-id/E1RdRfu-0004E9-8N@wrigleys.postgresql.org) > - was this ever fixed for 9.1.x? It was not, and won't be; the changes required to fix it properly seemed too invasive to back-patch, especially considering that you can easily avoid the bug. regards, tom lane Author: Tom Lane <tgl@sss.pgh.pa.us> Branch: master Release: REL9_2_BR [e2c2c2e8b] 2011-12-23 18:45:14 -0500 Improve planner's handling of duplicated index column expressions. It's potentially useful for an index to repeat the same indexable column or expression in multiple index columns, if the columns have different opclasses. (If they share opclasses too, the duplicate column is pretty useless, but nonetheless we've allowed such cases since 9.0.) However, the planner failed to cope with this, because createplan.c was relying on simple equal() matching to figure out which index column each index qual is intended for. We do have that information available upstream in indxpath.c, though, so the fix is to not flatten the multi-level indexquals list when putting it into an IndexPath. Then we can rely on the sublist structure to identify target index columns in createplan.c. There's a similar issue for index ORDER BYs (the KNNGIST feature), so introduce a multi-level-list representation for that too. This adds a bit more representational overhead, but we might more or less buy that back by not having to search for matching index columns anymore in createplan.c; likewise btcostestimate saves some cycles. Per bug #6351 from Christian Rudolph. Likely symptoms include the "btree index keys must be ordered by attribute" failure shown there, as well as "operator MMMM is not a member of opfamily NNNN". Although this is a pre-existing problem that can be demonstrated in 9.0 and 9.1, I'm not going to back-patch it, because the API changes in the planner seem likely to break things such as index plugins. The corner cases where this matters seem too narrow to justify possibly breaking things in a minor release. Author: Tom Lane <tgl@sss.pgh.pa.us> Branch: master Release: REL9_2_BR [472d3935a] 2011-12-24 19:03:21 -0500 Rethink representation of index clauses' mapping to index columns. In commit e2c2c2e8b1df7dfdb01e7e6f6191a569ce3c3195 I made use of nested list structures to show which clauses went with which index columns, but on reflection that's a data structure that only an old-line Lisp hacker could love. Worse, it adds unnecessary complication to the many places that don't much care which clauses go with which index columns. Revert to the previous arrangement of flat lists of clauses, and instead add a parallel integer list of column numbers. The places that care about the pairing can chase both lists with forboth(), while the places that don't care just examine one list the same as before. The only real downside to this is that there are now two more lists that need to be passed to amcostestimate functions in case they care about column matching (which btcostestimate does, so not passing the info is not an option). Rather than deal with 11-argument amcostestimate functions, pass just the IndexPath and expect the functions to extract fields from it. That gets us down to 7 arguments which is better than 11, and it seems more future-proof against likely additions to the information we keep about an index path.
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