Re: optimizing db for small table with tons of updates - Mailing list pgsql-performance

Dear Kenji,

we had similar issuse with a banner impression update system,
that had high concurrency. we modfied the system to use insert
instead of update of the same row. performance wise things are
much better , but you have to keep deleting old data.

hope you extrapolate what i mean if its applicable to your case.

Regds
Rajesh Kumar Mallah

On 4/3/06, Kenji Morishige <kenjim@juniper.net> wrote:
> I am using postgresql to be the central database for a variety of tools for
> our testing infrastructure. We have web tools and CLI tools that require access
> to machine configuration and other states for automation.  We have one tool that
> uses a table that looks like this:
>
> systest_live=# \d cuty
>                 Table "public.cuty"
>    Column    |           Type           | Modifiers
> -------------+--------------------------+-----------
>  resource_id | integer                  | not null
>  lock_start  | timestamp with time zone |
>  lock_by     | character varying(12)    |
>  frozen      | timestamp with time zone |
>  freeze_end  | timestamp with time zone |
>  freeze_by   | character varying(12)    |
>  state       | character varying(15)    |
> Indexes:
>     "cuty_pkey" PRIMARY KEY, btree (resource_id)
>     "cuty_main_idx" btree (resource_id, lock_start)
> Foreign-key constraints:
>     "cuty_resource_id_fkey" FOREIGN KEY (resource_id) REFERENCES resource(resource_id) ON UPDATE CASCADE ON DELETE
CASCADE
>
> Various users run a tool that updates this table to determine if the particular
> resource is available or not.  Within a course of a few days, this table can
> be updated up to 200,000 times.  There are only about 3500 records in this
> table, but the update and select queries against this table start to slow
> down considerablly after a few days.  Ideally, this table doesn't even need
> to be stored and written to the filesystem.  After I run a vacuum against this
> table, the overall database performance seems to rise again.  When database
> is running with recent vacuum the average server load is about .40, but after
> this table is updated 200,000+ times, the server load can go up to 5.0.
>
> here is a typical update query:
> 2006-04-03 10:53:39 PDT testtool systest_live kyoto.englab.juniper.net(4888) LOG:  duration: 2263.741 ms  statement:
UPDATEcuty SET 
>          lock_start = NOW(),
>          lock_by = 'tlim'
>         WHERE resource_id='2262' and (lock_start IS NULL OR lock_start < (NOW() - interval '3600 second'))
>
> We used to use MySQL for these tools and we never had any issues, but I believe
> it is due to the transactional nature of Postgres that is adding an overhead
> to this problem.  Are there any table options that enables the table contents
> to be maintained in ram only or have delayed writes for this particular table?
>
> Thanks in advance,
> Kenji
>
> ---------------------------(end of broadcast)---------------------------
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>