On Fri, May 25, 2012 at 4:58 AM, Greg Spiegelberg <gspiegelberg@xxxxxxxxx> wrote:On Sun, May 13, 2012 at 10:01 AM, Craig James <cjames@xxxxxxxxxxxxxx> wrote:On Sun, May 13, 2012 at 1:12 AM, Віталій Тимчишин <tivv00@xxxxxxxxx> wrote:The sequences AFAIK are accounted as relations. Large list of relations may slowdown different system utilities like vacuuming (or may not, depends on queries and indexes on pg_class).
Not "may slow down." Change that to "will slow down and possibly corrupt" your system.
In my experience (PG 8.4.x), the system can handle in the neighborhood of 100,000 relations pretty well. Somewhere over 1,000,000 relations, the system becomes unusable. It's not that it stops working -- day-to-day operations such as querying your tables and running your applications continue to work. But system operations that have to scan for table information seem to freeze (maybe they run out of memory, or are encountering an O(N^2) operation and simply cease to complete).
Glad I found this thread.Is this 1M relation mark for the whole database cluster or just for a single database within the cluster?
I don't know. When I discovered this, our system only had a few dozen databases, and I never conducted any experiments. We had to write our own version of pg_dump to get the data out of the damaged system, and then reload from scratch. And it's not a "hard" number. Even at a million relation things work ... they just bog down dramatically. By the time I got to 5 million relations (a rogue script was creating 50,000 tables per day and not cleaning up), the system was effectively unusable.
This is somewhat disturbing. I need to throw out a question I hope for an answer.
Has anyone ever witnessed similar behavior with a large number of relations? Slow? Corruption?
-Greg
