Thread: (9.1) btree_gist support for searching on "not equals"
This patch adds support to btree_gist for searching on <> ("not
equals").
This allows an interesting use of exclusion constraints:
Say you have a table:
create table zoo
(
cage int,
animal text,
exclude using gist (cage with =, animal with <>)
);
That will permit you to add as many zebras as you want to a given cage,
and as many lions as you want to another cage, but will not allow you to
mix zebras and lions in the same cage.
It also allows you to enforce the constraint that only one tuple exists
in a table by doing something like:
create table a
(
i int,
exclude using gist (i with <>),
unique (i)
);
Regards,
Jeff Davis
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On 5/21/10 11:47 PM +0300, Jeff Davis wrote: > It also allows you to enforce the constraint that only one tuple exists > in a table by doing something like: > > create table a > ( > i int, > exclude using gist (i with<>), > unique (i) > ); FWIW, this is achievable a lot more easily: CREATE UNIQUE INDEX "a_single_row" ON a ((1)); Regards, Marko Tiikkaja
Marko Tiikkaja <marko.tiikkaja@cs.helsinki.fi> wrote: > On 5/21/10 11:47 PM +0300, Jeff Davis wrote: > > It also allows you to enforce the constraint that only one tuple exists > > in a table by doing something like: > > > > create table a > > ( > > i int, > > exclude using gist (i with<>), > > unique (i) > > ); +1. I've not read the code, but it might be considerable that we can abort index scans if we find a first index entry for "i". While we must scan all candidates for "WHERE i <> ?", but we can abort for the constraint case because we know existing values are all the same. > FWIW, this is achievable a lot more easily: > CREATE UNIQUE INDEX "a_single_row" ON a ((1)); The former exclusion constraint means "one same value for all rows", but your alternative means "a_single_row", right? Regards, --- Takahiro Itagaki NTT Open Source Software Center
On Sat, 2010-05-22 at 01:02 +0300, Marko Tiikkaja wrote: > On 5/21/10 11:47 PM +0300, Jeff Davis wrote: > > It also allows you to enforce the constraint that only one tuple exists > > in a table by doing something like: > > > > create table a > > ( > > i int, > > exclude using gist (i with<>), > > unique (i) > > ); > > FWIW, this is achievable a lot more easily: > CREATE UNIQUE INDEX "a_single_row" ON a ((1)); > Yes, you're right. Also, neither of us accounted for NULLs, so I suppose a NOT NULL is necessary as well. I think the original case (same values only) is potentially useful enough that we should support it. Regards,Jeff Davis
On Mon, May 24, 2010 at 11:25 PM, Jeff Davis <pgsql@j-davis.com> wrote: > I think the original case (same values only) is potentially useful > enough that we should support it. +1. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company
(1) Exclusion constraints support for operators where "x <operator> x" is false (tiny patch) https://commitfest.postgresql.org/action/patch_view?id=307 (2) btree_gist support for searching on <> ("not equals") https://commitfest.postgresql.org/action/patch_view?id=308 Those patches should be committed at once because (2) requires (1) to work with EXCLUDE constraints. Also, (1) has no benefits without (2) because we have no use cases for <> as an index-able operator. Both patches are very simple and small, and worked as expected both "WHERE <>" and EXCLUDE constraints cases. I'd like to ask you to write additional documentation about btree_gist [1] that the module will be more useful when it is used with exclusion constraints together. Without documentation, no users find the usages. Of course the docs can be postponed if you have a plan to write docs when PERIOD types are introduced, [1] http://developer.postgresql.org/pgdocs/postgres/btree-gist.html The patch was not applied to 9.0, but the reason was just "no time to test" [2]. We have enough time to test for 9.1, so we can apply it now! [2] http://archives.postgresql.org/pgsql-hackers/2010-05/msg01874.php -- Itagaki Takahiro
Hi, Thank you for the review. On Mon, 2010-07-12 at 17:17 +0900, Itagaki Takahiro wrote: > (1) Exclusion constraints support for operators where "x <operator> x" > is false (tiny patch) > https://commitfest.postgresql.org/action/patch_view?id=307 > (2) btree_gist support for searching on <> ("not equals") > https://commitfest.postgresql.org/action/patch_view?id=308 > > Those patches should be committed at once because (2) requires (1) to work > with EXCLUDE constraints. Also, (1) has no benefits without (2) because we > have no use cases for <> as an index-able operator. Both patches are very > simple and small, and worked as expected both "WHERE <>" and EXCLUDE > constraints cases. It appears that Tom already committed (1). > I'd like to ask you to write additional documentation about btree_gist [1] > that the module will be more useful when it is used with exclusion > constraints together. Without documentation, no users find the usages. Good idea, new patch attached. Regards, Jeff Davis
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2010/7/16 Jeff Davis <pgsql@j-davis.com>: >> I'd like to ask you to write additional documentation about btree_gist [1] >> that the module will be more useful when it is used with exclusion >> constraints together. Without documentation, no users find the usages. | Example using an Exclusion Constraint to enforce the constraint | that a cage at a zoo can contain only one kind of animal: Very interesting example :-) The patch will be applied immediately. -- Itagaki Takahiro
On Fri, Jul 16, 2010 at 1:19 AM, Jeff Davis <pgsql@j-davis.com> wrote: > Thank you for the review. > > On Mon, 2010-07-12 at 17:17 +0900, Itagaki Takahiro wrote: >> (1) Exclusion constraints support for operators where "x <operator> x" >> is false (tiny patch) >> https://commitfest.postgresql.org/action/patch_view?id=307 >> (2) btree_gist support for searching on <> ("not equals") >> https://commitfest.postgresql.org/action/patch_view?id=308 >> >> Those patches should be committed at once because (2) requires (1) to work >> with EXCLUDE constraints. Also, (1) has no benefits without (2) because we >> have no use cases for <> as an index-able operator. Both patches are very >> simple and small, and worked as expected both "WHERE <>" and EXCLUDE >> constraints cases. > > It appears that Tom already committed (1). > >> I'd like to ask you to write additional documentation about btree_gist [1] >> that the module will be more useful when it is used with exclusion >> constraints together. Without documentation, no users find the usages. > > Good idea, new patch attached. It seems pretty odd to define a constant called BTNotEqualStrategyNumber in contrib/btree_gist. Shouldn't we either call this something else, or define it in access/skey.h? Considering that there seem to be some interesting gymnastics being done with BTMaxStrategyNumber, I'd vote for the former. Maybe just BtreeGistNotEqualStrategyNumber? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company
On Sun, 2010-08-01 at 21:57 -0400, Robert Haas wrote: > On Fri, Jul 16, 2010 at 1:19 AM, Jeff Davis <pgsql@j-davis.com> wrote: > > Thank you for the review. > > > > On Mon, 2010-07-12 at 17:17 +0900, Itagaki Takahiro wrote: > >> (1) Exclusion constraints support for operators where "x <operator> x" > >> is false (tiny patch) > >> https://commitfest.postgresql.org/action/patch_view?id=307 > >> (2) btree_gist support for searching on <> ("not equals") > >> https://commitfest.postgresql.org/action/patch_view?id=308 > >> > >> Those patches should be committed at once because (2) requires (1) to work > >> with EXCLUDE constraints. Also, (1) has no benefits without (2) because we > >> have no use cases for <> as an index-able operator. Both patches are very > >> simple and small, and worked as expected both "WHERE <>" and EXCLUDE > >> constraints cases. > > > > It appears that Tom already committed (1). > > > >> I'd like to ask you to write additional documentation about btree_gist [1] > >> that the module will be more useful when it is used with exclusion > >> constraints together. Without documentation, no users find the usages. > > > > Good idea, new patch attached. > > It seems pretty odd to define a constant called > BTNotEqualStrategyNumber in contrib/btree_gist. Shouldn't we either > call this something else, or define it in access/skey.h? Considering > that there seem to be some interesting gymnastics being done with > BTMaxStrategyNumber, I'd vote for the former. Maybe just > BtreeGistNotEqualStrategyNumber? Sounds good to me. At some point we may be interested to add this to BTree, as well. But we can cross that bridge when we come to it. Regards,Jeff Davis
On Mon, Aug 2, 2010 at 2:39 AM, Jeff Davis <pgsql@j-davis.com> wrote: > On Sun, 2010-08-01 at 21:57 -0400, Robert Haas wrote: >> On Fri, Jul 16, 2010 at 1:19 AM, Jeff Davis <pgsql@j-davis.com> wrote: >> > Thank you for the review. >> > >> > On Mon, 2010-07-12 at 17:17 +0900, Itagaki Takahiro wrote: >> >> (1) Exclusion constraints support for operators where "x <operator> x" >> >> is false (tiny patch) >> >> https://commitfest.postgresql.org/action/patch_view?id=307 >> >> (2) btree_gist support for searching on <> ("not equals") >> >> https://commitfest.postgresql.org/action/patch_view?id=308 >> >> >> >> Those patches should be committed at once because (2) requires (1) to work >> >> with EXCLUDE constraints. Also, (1) has no benefits without (2) because we >> >> have no use cases for <> as an index-able operator. Both patches are very >> >> simple and small, and worked as expected both "WHERE <>" and EXCLUDE >> >> constraints cases. >> > >> > It appears that Tom already committed (1). >> > >> >> I'd like to ask you to write additional documentation about btree_gist [1] >> >> that the module will be more useful when it is used with exclusion >> >> constraints together. Without documentation, no users find the usages. >> > >> > Good idea, new patch attached. >> >> It seems pretty odd to define a constant called >> BTNotEqualStrategyNumber in contrib/btree_gist. Shouldn't we either >> call this something else, or define it in access/skey.h? Considering >> that there seem to be some interesting gymnastics being done with >> BTMaxStrategyNumber, I'd vote for the former. Maybe just >> BtreeGistNotEqualStrategyNumber? > > Sounds good to me. OK, committed that way. > At some point we may be interested to add this to BTree, as well. But we > can cross that bridge when we come to it. Yeah. I was also wondering if it would be worth adding some additional regression testing to contrib/btree_gist exercising this new functionality. Thoughts? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company
On Mon, 2010-08-02 at 12:27 -0400, Robert Haas wrote:
> I was also wondering if it would be worth adding some additional
> regression testing to contrib/btree_gist exercising this new
> functionality. Thoughts?
Sure. I attached two tests.
Regards,
Jeff Davis
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On Mon, Aug 2, 2010 at 11:16 PM, Jeff Davis <pgsql@j-davis.com> wrote: > On Mon, 2010-08-02 at 12:27 -0400, Robert Haas wrote: >> I was also wondering if it would be worth adding some additional >> regression testing to contrib/btree_gist exercising this new >> functionality. Thoughts? > > Sure. I attached two tests. Committed. I renamed the test to "not_equals" rather than "mixed" and added an "EXPLAIN (COSTS OFF)" in there to verify that the index is actually being used. (I might have to remove that if it turns out not to be stable between an index scan and a bitmap index scan, but let's see what the buildfarm says.) -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company
Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Aug 2, 2010 at 11:16 PM, Jeff Davis <pgsql@j-davis.com> wrote:
>> Sure. I attached two tests.
> Committed.
I see no sign of a commit from here ...
regards, tom lane
On Tue, Aug 3, 2010 at 3:52 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote: > Robert Haas <robertmhaas@gmail.com> writes: >> On Mon, Aug 2, 2010 at 11:16 PM, Jeff Davis <pgsql@j-davis.com> wrote: >>> Sure. I attached two tests. > >> Committed. > > I see no sign of a commit from here ... Sigh. Forgot to exit my editor. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company