I would consider mine a small setup on an internal network and I have used
both Sybase and SQL Server. In our case the DBA's preferred us to remain
connected rather than make too many connections - we need DB access in
bursts - it could be quiet for more than an hour and then suddenly we might
need hundreds of connections within few minutes (if we didnt cache it).
Another thing was we were connecting from forked processes so at some point
everything gets reaped including the connections. Our style of coding has
been to connect to the DB wherever we actually need to fire one or more
SQLs and do connect_cached in the actual implementation (it is a separate
library since we had to place a wrapper to acquire credentials)
On Tue, Feb 9, 2021 at 2:34 PM James Smith <j...@sanger.ac.uk> wrote:
> Mithun,
>
> I’m not sure on what scale you work – but these are from experience in
> sites with small to medium load – and we rarely see an appreciable gain in
> using cached or pooled connections, just the occasional heartache they
> cause.
> If you are working on small applications with a minimal number of
> databases on the DB server then you may see some performance improvement
> (but tbh not as much as you used to – as the servers have changed)
> Unfortunately I don’t in both my main and secondary roles, and I know many
> others who come across these limitations as well.
>
> I’m not saying don’t use persistent or cached connections – but leaving it
> to some hidden layers is not necessarily a good thing to do – it can have
> unforeseen side effects {and Apache::DBI & PHP pconnect have both shown
> these up}
>
> If you are working with e.g. with MySQL the overhead of the (socket)
> connection is very small, but having more connections open to cope with
> persistent connections {memory wise} often needs specifying a much large
> database server – or not being able to do all the nice tricks to in memory
> indexes and queries [to increase query performance]. Being able to chose
> which connections you keep open and which you open/close on a per request
> basis gives you the benefits of caching without the risks involved [other
> than the “lock table” issue].
>
>
>
>
>
> *From:* Mithun Bhattacharya <mit...@gmail.com>
> *Sent:* 09 February 2021 18:34
> *To:* mod_perl list <modperl@perl.apache.org>
> *Subject:* Re: Moving ExecCGI to mod_perl - performance and custom
> 'modules' [EXT]
>
>
>
> Connection caching does work for most use cases - we have to accept James
> works in scenarios most developers can't fathom :)
>
>
>
> If you are just firing off simple SQL's without any triggers or named
> temporary tables involved you should be good. The only times we recall
> tripping on cached connection is when two different code snippets tried to
> create the same temporary table. Another time the code was expecting the
> disconnect to complete the connection cleanup.
>
>
>
> On Tue, Feb 9, 2021 at 11:47 AM Vincent Veyron <vv.li...@wanadoo.fr>
> wrote:
>
> On Sun, 7 Feb 2021 20:21:34 +0000
> James Smith <j...@sanger.ac.uk> wrote:
>
> Hi James,
>
> > DBI sharing doesn't really gain you much - and can actually lead you
> into a whole world of pain. It isn't actually worth turning it on at all.
> >
>
> Never had a problem with it myself in years of using it, but I wrap my
> queries in an eval { } and check $@, so that the scripts are not left
> hanging; also I have a postgresql db ;-).
>
> I ran some tests with ab, I do see an improvement in response speed :
>
> my $dbh = DBI->connect()
> Concurrency Level: 5
> Time taken for tests: 22.198 seconds
> Complete requests: 1000
> Failed requests: 0
> Total transferred: 8435000 bytes
> HTML transferred: 8176000 bytes
> Requests per second: 45.05 [#/sec] (mean)
> Time per request: 110.990 [ms] (mean)
> Time per request: 22.198 [ms] (mean, across all concurrent requests)
> Transfer rate: 371.08 [Kbytes/sec] received
>
> my $dbh = DBI->connect_cached()
> Concurrency Level: 5
> Time taken for tests: 15.133 seconds
> Complete requests: 1000
> Failed requests: 0
> Total transferred: 8435000 bytes
> HTML transferred: 8176000 bytes
> Requests per second: 66.08 [#/sec] (mean)
> Time per request: 75.664 [ms] (mean)
> Time per request: 15.133 [ms] (mean, across all concurrent requests)
> Transfer rate: 544.33 [Kbytes/sec] received
>
>
> --
>
> Bien à vous, Vincent Veyron
>
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