Re: PostgresSQL vs. Informix

Chad --
<...>
>
> Have you seen any studies (either by Sun or others) that compares
> PostgresSQL to other commercial database software (Informix, Oracle,
> Sybase,etc.)? I am interested seeing a feature by feature comparison of
> PostgresSQL and Informix.
>

Hope this ain't too late!

I can't provide a feature by feature comparison and I've never seen benchmarks comparing Informix to PostgreSQL.

I can however speak from the experience of having migrated a moderate sized set of databases from Informix 9.x to PostgreSQL. Alas, we went from Sun Solaris with Informix to Linux with PostgreSQL so a direct comparison is not realistic. But in most things we have found the two roughly the same; when there are differences Informix has usually been faster but not always.

A few almost random points in now particular order, in addition to what other posters have said:

* SQL is fairly similar with some exceptions
DISTINCT vs UNIQUE; see also DISTINCT ON; Informix handles NULLs in
concatenations differently (see COALESCE in PostgreSQL SQL); LIMIT
is handled differently. UPDATE STATISTICS is roughly like ANALYZE.

* MVCC has some real differences; in particular SELECT COUNT(*) FROM foo;
is noticibly slower in PostgreSQL (but much less so in 8.3beta).
Read the manual sections on autovacuum/vacuum carefully. Logging differs
as well. Rollbacks are cheaper in PostreSQL.

* Beware the default settings on PostgreSQL configs -- they are very
conservative and can lead to performance issues if you don't
tweak them.

* High speed loader is slightly faster than COPY FROM, but not by a lot.

* SPL conversion is a pain and I've basically recoded everything, although
it gets easiers once you get used to the differences (returning set
values for instance). Only had a few dozen procedures had to get done.

* We use the PostGIS spatial extension (akin to the Spatial Blade in Informix)
Informix had better documentation, and a bit more functionality, but
if a spatial user defined function went bad it could (and would) bring
the whole instance down with a hard crash; rebooting the server was often
necessary. The very few times we've seen PostGIS slay a PostgreSQL instance,
the PostgreSQL recovery way far easier -- sometimes not even needing a recycle.
YMMV

* Informix's replication and backups are superior. But for most purposes I think
PostgreSQL has a usable variant. But certainly not for all needs.

* PostgreSQL spawns a process for each connection (make sure you tweak shared
memory!); this leads to higher apparent loads and lots more processes in
a "ps" or "top" listing than you'd see on an Informix database server since
Informix uses internal threads. But throughput is the metric ...

* There is no such thing as raw disk space in PostgreSQL; the claim is it doesn't
gain them much since modern OSs have spent a lot of time on regular file
system speed; the argument goes on that when Informix and Oracle were young
so were the servers they were on, and they had to invent everything for
themselves.

* There is no equivalent of a "synonym"; a view can be used to fake this sometimes
but where Informix lets you create a synonym to a table in another database /
instance, PostgreSQL doesn't. dblink can be used to poke a hole to other
databases though, including non-postgres ones.

* Locking differs some -- no such thing as a page level lock.

HTH -- might add more if I think of anything.

Greg Williamson
Senior DBA
GlobeXplorer LLC, a DigitalGlobe company

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