Michael wrote:
> I have two instances of a production application that uses Postgres
> deployed in two different data centers for about the last 6 months.
> sizes, schemas, configurations, hardware, and access patterns of the
> databases are nearly identical, but one consistently takes at least 5x
> longer than the other for some common operations.  During this time,
> usage and IO on the slow database are both high (sustained); I'm not
> sure about the fast database.  These common operations are chatty - at
> least tens of thousands of queries over a 5 to 60 minute stretch - but
> the queries themselves are fairly simple.  The query plans are
> across both databases, and the data distribution is comparable.  The
> tables involved in these common operations change frequently, and are
> indexed according to these queries.  The queries use the indexes as
> expected.  The tables involved have 50k-500k rows.

Have you isolated any hardware issues?  For example, if you are using
ATA cables, and one is kinked or too long, you could be having ATA
errors which cause bizarre and intermittent slowdowns and pauses,
especially in raid systems.  Do a filesystem diagnostic to check this.


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