Re: strange performance regression between 7.4 and 8.1

[Jeff Frost <jeff(at)frostconsultingllc(dot)com>]

On Thu, 1 Mar 2007, Alex Deucher wrote:

> > Vacuum? Analayze? default_statistics_target? How many shared_buffers?
> > effective_cache_size? work_mem?
>
> I'm running the autovacuum process on the 8.1 server.  vacuuming on
> the old server was done manually.
>
> default_statistics_target and effective_cache_size are set to the the
> defaults on both.
>
> postgres 7.4 server:
> # - Memory -
> shared_buffers = 82000 # 1000            min 16, at least
> max_connections*2, 8KB each
> sort_mem = 8000        # 1024            min 64, size in KB
> vacuum_mem = 32000     # 8192            min 1024, size in KB
> # - Free Space Map -
> #max_fsm_pages = 20000          # min max_fsm_relations*16, 6 bytes each
> #max_fsm_relations = 1000       # min 100, ~50 bytes each
> # - Kernel Resource Usage -
> #max_files_per_process = 1000   # min 25
>
> postgres 8.1 server:
> # - Memory -
> shared_buffers = 100000                 # min 16 or max_connections*2, 8KB 
> each
> temp_buffers = 2000 #1000                       # min 100, 8KB each
> max_prepared_transactions = 100 #5              # can be 0 or more
> # note: increasing max_prepared_transactions costs ~600 bytes of shared 
> memory
> # per transaction slot, plus lock space (see max_locks_per_transaction).
> work_mem = 10000        #1024           # min 64, size in KB
> maintenance_work_mem = 524288 #16384            # min 1024, size in KB
> #max_stack_depth = 2048                 # min 100, size in KB
>
> I've also tried using the same settings from the old server on the new
> one; same performance issues.

If this is a linux system, could you give us the output of the 'free' command? 
Postgresql might be choosing a bad plan because your effective_cache_size is 
way off (it's the default now right?).  Also, what was the block read/write 
speed of the SAN from your bonnie tests?  Probably want to tune 
random_page_cost as well if it's also at the default.


--
Jeff Frost, Owner 	<jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC 	http://www.frostconsultingllc.com/
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