Re: Using a single database handle or multiple handles

[tobyink]

Depends on the database. For most, a single handle is preferable.

Microsoft SQL Server (and presumably Sybase too), when connected to using the TDS libraries does not allow multiple concurrent queries to execute on the same handle. You need to finish one query before making another. Thus patterns where you do:

my $results = $dbh->someQuery;
while (my $row = $results->fetchrow_array)
{
  $dbh->someOtherQuery;
}

will not work unless you open a second connection. (I think some newer versions of TDS do actually emulate concurrent queries by transparently opening a second connection when required.)

[mje]

Newer MS SQL Server drivers (and some other commercial ones) have an attribute called MARS_Connection which when set to 1 enables Multiple Active Result Sets. However, it is generally slower and has a number of restrictions. I wrote a small article on it for DBD::ODBC at Multiple Active Statements (MAS) and DBD::ODBC.