A few links regarding comparisons of PostgreSQL vs. MySQL.
The general consensus seems to be the MySQL is fast but very slightly
flaky and may have scaling problems. PostgreSQL is slower under low
loads, but getting better, and may perform better than MySQL under heavy
loads.
Really, the only way to find out is to try both and compare.
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From:
http://linux.oreillynet.com/pub/a/linux/2002/01/31/worldforge.html?page=2
Quotes:
Riddoch:
"MySQL performs poorly under a heavy load," he says. "In particular, it
does not handle very large tables well and does not optimize complex
queries well.
Harrington:
"For read-only applications [PostgreSQL] can be significantly slower
than MySQL, but we have not done any benchmarking or timing so we can't
really say much there.
http://www.mysql.com/information/benchmarks.html
shows MySQL generally outperforming PostgreSQL on simple reads.
http://www.cbbrowne.com/info/rdbmssql.html
mostly critiques MySQL as unstable compared to other databases
http://osdb.sourceforge.net/
the Open Source Database Benchmark
http://openacs.org/philosophy/why-not-mysql.html
generally criticises MySQL!