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From "Giulio Cesare Solaroli" <giulio.ces...@gmail.com>
Subject Re: Optimize cascade deletes
Date Tue, 02 Oct 2007 07:02:55 GMT
Hello Tore,

On 10/2/07, Tore Halset <halset@pvv.ntnu.no> wrote:
> Hello.
>
> This does not sound like a cayenne issue any more.

Definitely.


> Here is what I would do to get going.
>
>   * Remove the extra OS layer if you are still using it. Was it
> Parallells?

Parallels could alter the absolute values of the operation timing; but
I have see an consistent difference between 20 and 100 times faster on
the newly created table; this make me think that it is not a problem
bound to the usage of a virtual machine.


>   * Update to latest PostgreSQL and JDBC driver.

I may try to update to the latest PostgreSQL version, but it is not a
JDBC issue as I got the same problem issuing the query right from
psql.


>   * Use vacuum analyze and autovacuum

I have already tried this.


>   * Find slow queries and use "explain <query>"

The slow query is a simple delete on a table accessed using the
primary key. The explain plan reports an index scan, as expected.


>   * Make sure PostgreSQL are set up with enough memory.

The current instance i probably running with a very low memory
footprint, but if a copy of the same table on the same PostgreSQL
instance is running the same query 20 to 100 times faster, there is
something else to fix before tuning the memory.


>   * Ask on pgsql-performance@postgresql.org

Great pointer. Thanks!!!! :-)

Best regards,

Giulio Cesare




> On Oct 1, 2007, at 19:05 , Giulio Cesare Solaroli wrote:
>
> > Yes,
> >
> > I have vacuumed it and also rebuild the indexes to no avail. :-(
> >
> > I am not a PostgreSQL expert (and not even an expert DBA in general),
> > so it is very possible that I am doing something very wrong.
> >
> > This is both a good news (the application should be fine, and I don't
> > need to tune it much further) and bad news (I need to learn how to
> > tune a PostgreSQL db, or find someone that could help).
> >
> > Best regards,
> >
> > Giulio Cesare
> >
> >
> >
> >
> > On 10/1/07, Michael Gentry <blacknext@gmail.com> wrote:
> >> Have you vacuumed the original (slow) table?
> >>
> >> /dev/mrg
> >>
> >> On 10/1/07, Giulio Cesare Solaroli <giulio.cesare@gmail.com> wrote:
> >>> Hello everybody,
> >>>
> >>> today I have being able to do some more tests and I have found out
> >>> that the problem seems to be caused by a "fragmentation" of the data
> >>> on the Postgresql table space.
> >>>
> >>> I have created a copy of the table where delete statements where
> >>> very
> >>> slow (using the "create table .... as select from ..." syntax) and
> >>> matching the structure of the new copy to the original one (index
> >>> and
> >>> constraint wise); in this new table the performance of the delete
> >>> statements where from 20 to 100 times faster that in the original
> >>> table. :-(
> >>>
> >>> This rules out Cayenne as the culprit, but leave me wondering how to
> >>> avoid this degradation of performances on Postgresql; but this is
> >>> probably not the right place where to start.
> >>>
> >>> Thank you everybody for your attention and for the very useful
> >>> suggestions or pointers that greatly helped me in understanding this
> >>> problem.
> >>>
> >>> Best regards,
> >>>
> >>> Giulio Cesare
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> On 9/23/07, Giulio Cesare Solaroli <giulio.cesare@gmail.com> wrote:
> >>>> Hello,
> >>>>
> >>>> I have collected a few more data, as suggested by Aristedes.
> >>>>
> >>>> On 9/23/07, Giulio Cesare Solaroli <giulio.cesare@gmail.com> wrote:
> >>>>> On 9/23/07, Aristedes Maniatis <ari@maniatis.org> wrote:
> >>>>>>
> >>>>>> On 23/09/2007, at 5:38 PM, Giulio Cesare Solaroli wrote:
> >>>>>>
> >>>>>>> log4j.logger.org.apache.cayenne=ERROR
> >>>>>>> log4j.logger.org.apache.cayenne.access.QueryLogger=DEBUG
> >>>>>>>
> >>>>>>>
> >>>>>>> Is there anything going on on the Cayenne code between the
> >>>>>>> last [batch
> >>>>>>> bind:xxx] log and the "updated" log?
> >>>>>>
> >>>>>> Well, you could always try:
> >>>>>>
> >>>>>> log4j.logger.org.apache.cayenne=DEBUG
> >>>>>
> >>>>> Argh. I should have thought about this myself. :-(
> >>>>
> >>>> Even with full log enabled I got the same exact log, so it looks
> >>>> like
> >>>> all the time is really spent on the DB. And the next logs confirm
> >>>> this.
> >>>>
> >>>>
> >>>>>>> Is all this time spent on the DB only?
> >>>>>>
> >>>>>> What does turning on log_min_duration_statement tell you?
> >>>>
> >>>> I have being able to run PostgreSQL with logging enabled only on my
> >>>> Parallels instance, as I can not start/stop the db on the
> >>>> deployment
> >>>> server; this will make the absolute times not that relevant, but I
> >>>> hope we can understand something more anyway.
> >>>>
> >>>> First of all, there is a huge difference between the deletion
> >>>> time of
> >>>> the "cascade" records in different tables.
> >>>>
> >>>> [...]
> >>>> LOG:  duration: 0.020 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM connection.USRCNNRQS WHERE ID_USRCNNRQS = $1]
> >>>> LOG:  duration: 0.021 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM connection.USRCNNRQS WHERE ID_USRCNNRQS = $1]
> >>>> LOG:  duration: 0.020 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM connection.USRCNNRQS WHERE ID_USRCNNRQS = $1]
> >>>> [...]
> >>>>
> >>>> To delete rows on the USRCNNRQS (aka UserConnectionRequest)
> >>>> table, it
> >>>> averages at bout 0.020 ms.
> >>>>
> >>>>
> >>>> For another table (USRCNN aka UserConnection) the times range from
> >>>> 0.145 to 0.060, for later settling for 0.040 ms:
> >>>>
> >>>> [...]
> >>>> LOG:  duration: 0.090 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM connection.USRCNN WHERE ID_USRCNN = $1]
> >>>> LOG:  duration: 0.071 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM connection.USRCNN WHERE ID_USRCNN = $1]
> >>>> LOG:  duration: 0.067 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM connection.USRCNN WHERE ID_USRCNN = $1]
> >>>> [...]
> >>>>
> >>>>
> >>>> It later took 43 seconds (!!) to parse and execute the deletion
> >>>> of a
> >>>> single record, ...
> >>>> [...]
> >>>> LOG:  statement: PREPARE S_5 AS DELETE FROM clipperz.RCR WHERE
> >>>> ID_RCR = $1
> >>>> LOG:  statement: <BIND>
> >>>> LOG:  statement: EXECUTE <unnamed>  [PREPARE:  DELETE FROM
> >>>> clipperz.RCR WHERE ID_RCR = $1]
> >>>> LOG:  duration: 42.998 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM clipperz.RCR WHERE ID_RCR = $1]
> >>>> LOG:  statement: <BIND>
> >>>> LOG:  statement: EXECUTE <unnamed>  [PREPARE:  DELETE FROM
> >>>> clipperz.RCR WHERE ID_RCR = $1]
> >>>> [...]
> >>>>
> >>>> ...later spotting time as low as 0.042 for the execution of the
> >>>> same query:
> >>>> [...]
> >>>> LOG:  duration: 0.042 ms  statement: EXECUTE <unnamed>  [PREPARE:
> >>>> DELETE FROM clipperz.RCR WHERE ID_RCR = $1]
> >>>> LOG:  statement: <BIND>
> >>>> LOG:  statement: EXECUTE <unnamed>  [PREPARE:  DELETE FROM
> >>>> clipperz.RCR WHERE ID_RCR = $1]
> >>>> [...]
> >>>>
> >>>> But as I may understand this different timing may be due to the
> >>>> interaction of the Virtual machine with the real server, what is
> >>>> puzzling me is that the deletion from the latest table had a
> >>>> "constant" time of about 2 seconds each:
> >>>> [...]
> >>>> LOG:  duration: 1929.043 ms  statement: EXECUTE <unnamed>
> >>>> [PREPARE:
> >>>> DELETE FROM clipperz.RCRVRS WHERE ID_RCRVRS = $1]
> >>>> LOG:  duration: 1991.311 ms  statement: EXECUTE <unnamed>
> >>>> [PREPARE:
> >>>> DELETE FROM clipperz.RCRVRS WHERE ID_RCRVRS = $1]
> >>>> LOG:  duration: 2078.249 ms  statement: EXECUTE <unnamed>
> >>>> [PREPARE:
> >>>> DELETE FROM clipperz.RCRVRS WHERE ID_RCRVRS = $1]
> >>>> LOG:  duration: 2015.047 ms  statement: EXECUTE <unnamed>
> >>>> [PREPARE:
> >>>> DELETE FROM clipperz.RCRVRS WHERE ID_RCRVRS = $1]
> >>>> [...]
> >>>>
> >>>>
> >>>> If nobody as something else to suggest, I will try to get back
> >>>> the the
> >>>> DB schema to see if there is some constraint/index that is slowing
> >>>> down the deletion of these records.
> >>>>
> >>>> Thank you very much for your attention.
> >>>>
> >>>> Best regards,
> >>>>
> >>>> Giulio Cesare
> >>>>
> >>>
> >>
> >
>
>

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