local & DBD::mysql

shemp has asked for the wisdom of the Perl Monks concerning the following question:

Update:Within the code block

Hi all. Simple question.

Is it advisable to use local to temporarily modify parts of a DBD::MySQL db handle for the 1 place in a big program where i want to use a transaction, or is this not going to work like i think?

   my $dbh = ...;
   ...
   { # enclosing block for transaction
#       local $dbh->{'AutoCommit'} = 1;
# UPDATE - thanks Corion
       local $dbh->{'AutoCommit'} = 0;
       local $dbh->{'PrintError'} = 0;

       # do the transaction queries
       ...
       $dbh->commit();
   }
[download]

What im trying to accomplish is the localized change of the $dbh attributes to do the transaction, then commit it. So as i see it, when i exit the enclosing block, the localized values will go out of scope and the originals will be restored. In reality, the enclosing block will be a function, but i wanted as simple an example as possible.

I already wrote a little test script that seems to work properly, but i am new to transactions, and dont use local that much, and am looking for any possible problems that this may cause.

I am mostly using whats in the MySQL cookbook section 15.4 Using Transactions in Perl Programs, but they dont use local, and using local seems cleaner to me.

Comment on local & DBD::mysql Download Code

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Re: local & DBD::mysql by Corion (Patriarch) on Jun 14, 2005 at 21:22 UTC
One caveat, as gleaned from the Class::DBI source code - this approach seems to leak memory "on older perls", whatever versions that might be. Other than that, I think your approach is fine, as it does automagic cleanup/restoration of the previous state. I think that you got the `AutoCommit` thing wrong though - AutoCommit should be a false value if you want to issue your transaction statements (begin transaction/commit transaction) yourself. But DBI will warn you about ineffective commit statements anyway.	[reply]
Re^2: local & DBD::mysql by shemp (Deacon) on Jun 14, 2005 at 21:26 UTC
For this particular app, im using perl v5.8.0 for sun4-solaris, so the memory leak probably wont be an issue - i hope.	[reply]
Re^3: local & DBD::mysql by polettix (Vicar) on Jun 15, 2005 at 16:34 UTC
There were memory leaks in v5.8.0 as I learnt from this post; BTW this specific problem was solved in v5.8.6 (don't know which release solved it actually). They're probably unrelated memory leak problems, but I wouldn't bet on v5.8.0 not leaking. Flavio (perl -e 'print(scalar(reverse("\nti.xittelop\@oivalf")))') Don't fool yourself.	[reply]