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(PostgreSQL:) Once you have a table 't' with a column 'hs' of type hstore, you can use statements like:

select * from t where hs ? 'x';

to do 'hash-lookups' (but there are many more hstore operators).

Below is a test program in bash/sql. It creates a table with an hstore with a million entries and indexes it.

Then a few searches to show the retrieval performance; same search repeated three times without index and then repeated three times with index:

$ pg_sql/pgsql.HEAD/hstore/ rowcount | size ----------+-------- 1000000 | 249 MB (1 row) Time: 183.026 ms Time: 184.673 ms Time: 183.903 ms Time: 0.295 ms Time: 0.245 ms Time: 0.274 ms

You see that the speedup is quite considerable :)

Here is that program:

(You must have hstore installed - see 'contrib' in older postgres or extensions in newer Pg's)

#!/bin/sh schema=public table=testhstore t=$schema.$table echo " --/* drop table if exists $t; create table $t ( hs hstore ); insert into $t select hstore(md5(cast(f.x as text)), cast(f.x as text)) from generate_series(1, 1000000) as f(x); create index ${table}_hs_idx on $t using gin (hs); analyze $t; --*/ select count(*) as rowcount, pg_size_pretty(pg_total_relation_size( '$ +{t}' )) as size from $t; " | psql -q v=9509342c6a6b283d07a3ce406b06eb1e # discard one run for cache effects, then run three times, no index: echo "set enable_bitmapscan=0; \o /dev/null select * from $t where hs ? '$v'; \o \timing on select * from $t where hs ? '$v'; select * from $t where hs ? '$v'; select * from $t where hs ? '$v';" \ | psql -q | grep -E '^Time:' # discard one run for cache effects, then run three times with index: echo "set enable_bitmapscan=1; \o /dev/null select * from $t where hs ? 'x'; \o \timing on select * from $t where hs ? '$v'; select * from $t where hs ? '$v'; select * from $t where hs ? '$v';" \ | psql -q | grep -E '^Time:'

Obviously we're far away from standard SQL here. Also from the OP's question, I think, but since you expressed interest I thought I'd construct an example. As always, there is much more in the Fine Manual:

(run on a pretty average 8120 desktop, slow single SATA disk, Centos 6.2 Linux, postgresql 9.3devel)

update: Changed to /dev/null redirection with \o inside a psql session. Also changed Timings from EXPLAIN ANALYZE to those from psql's '\timing on' (so I'm showing the slowest);

In reply to Re^4: Inserting Hash Information Into MySQL (PostgreSQL's hstore) by erix
in thread Inserting Hash Information Into MySQL by Anonymous Monk

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