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Re^4: SQLite with mod_perl

by punkish (Priest)
on Oct 09, 2010 at 02:12 UTC ( #864309=note: print w/ replies, xml ) Need Help??


in reply to Re^3: SQLite with mod_perl
in thread SQLite with mod_perl

Hi james2vegas, sorry for the delay in reply.

Well, I thought I had surmounted this problem, but no, it is back with a vengeance. Here is what is going on in a single web action --

SELECT col1 FROM table WHERE condition; if (col1 exists) { UPDATE table SET col2 = <new value> }

Well, I get the "db is locked" error at the UPDATE statement. Now, in my httpd.conf I started using

PerlModule Apache::DBI

and I thought my troubles were over. Except, this lock problem has started rearing up again. I have tried a few other things, such as starting every db action with $dbh->begin_work and ending with $dbh->commit, but I am already using AutoCommit => 1 so I am not sure if that even has any effect. I have even tried sqlite_use_immediate_transaction => 1, but that doesn't help either.

My application is being loaded in Apache conf file with

<Location /> SetHandler perl-script PerlHandler Plack::Handler::Apache2 PerlSetVar psgi_app /path/to/application.pl </Location>

So, I want all the perl modules to be loaded when Apache2 starts, and then a $dbh created for each user when the user comes to the web site, but not recreated for the same user on every reload. I am assuming that would be the correct way to work speedily.

--

when small people start casting long shadows, it is time to go to bed


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Re^5: SQLite with mod_perl
by james2vegas (Chaplain) on Oct 09, 2010 at 09:27 UTC
    Do not cache your database handles, rather let Apache::DBI take care of it, use Apache::DBI in your mod_perl startup script (or use PerlModule Apache::DBI in your httpd.conf) then whenever you need to open a database connection, do it as would normally my $dbh = DBI->connect(...). If you need connections per user add private_username => $username to your connection attributes, like so:
    my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile", "", "", { private_ +username => $username });
    This would ensure that each user would get a per-process database handle. Note that you can't share database handles across processes unless you use something single process like FastCGI.
      Hmmm... as I mentioned in my post above, I am indeed using  PerlModule Apache::DBI. Maybe I tinkered above (too smart for my own good) trying to cache the db handle. Now I am trying with just plain my $dbh = ... , and things seem to be working.

      One other thing I have done now -- I have turned off transactions. My db handle is now created with AutoCommit => 1.

      This is really unreliable. I have no idea what caused my app to start puking and croaking yesterday, and what caused it to start working today. I have become too dependent on SQLite (and for good reason -- it is a great db store), and I really don't know of any alternatives. Any suggestions? I could try some of the key-value stores such as MongoDB/CouchDB, etc., but it would require learning a whole new paradigm, and writing new code for retrieving values (is there a DBI interface to a key-value store? **) While I do use PostGres for the bigger datasets, SQLite seems perfect for serving as the Session store, and user accounts and such.

      Update: Hot damn! DBD::DBM

      --

      when small people start casting long shadows, it is time to go to bed

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