Re: Known problem with HASH index?

> Is there a known problem with HASH type index in PostgreSQL 7.1.2
> 4PGDG on Red Hat Linux 7.1 (2.4.2 kernel)?  I can't find a lot of
> documentation, but this is what I observe:

Tom Lane has mentioned several times that index types other than BTREE
have suffered some bit-rot over the past few years, and probably have
problems with concurrent access -- so using a BTREE is recommended
whenever possible. It would be cool if someone felt like taking the
time to clean up HASH indexes though...

> [playpen]$ dropdb test; createdb test; psql -f create_table.sql
> test; psql -c "COPY clients FROM '/tmp/input.txt';" test; psql -c
> 'CREATE INDEX clients_idx ON clients USING HASH (tel);' test;
> vacuumdb test; vacuumdb --analyze test DROP DATABASE

Doing vacuumdb followed by vacuumdb --analyze is redundant; doing a
VACUUM ANALYZE also does a regular VACUUM.

> NOTICE:  Index clients_idx: NUMBER OF INDEX' TUPLES (916864) IS NOT
> THE SAME AS HEAP' (1000000).
>  Recreate the index.

That's strange... Personally, I'd just switch to a BTREE, where
presumambly this won't occur. However, I'd suggest waiting for one of
the Postgres hackers to give you a proper answer ;-)

> [playpen]$ cat create_table.sql
> CREATE TABLE clients (
>        ClientID integer,
>        firstname varchar(5),
>        surname varchar(22),
>        area varchar(3),
>        neigh varchar(27),
>        dimos varchar(50),
>        tel varchar(7)

The missing ');' at the end is a typo, right?

> The input file is a bit big to include, but was created using this
> brain-damaged perl script (somebody please teach me how to do
> random letter strings :-))

Grab stuff from /usr/share/dict?

>srand(time||$$);

On modern Perls, the default srand() seed is more secure than this, I
believe. (Although it doesn't matter for your script, of course)

Cheers,

Neil