NAME

       DBIx::Class::Storage::DBI::Replicated::Pool - Manage a pool of replicants

SYNOPSIS

       This class is used internally by DBIx::Class::Storage::DBI::Replicated.  You shouldn't
       need to create instances of this class.

DESCRIPTION

       In a replicated storage type, there is at least one replicant to handle the read-only
       traffic.  The Pool class manages this replicant, or list of replicants, and gives some
       methods for querying information about their status.

ATTRIBUTES

       This class defines the following attributes.

   maximum_lag ($num)
       This is a number which defines the maximum allowed lag returned by the "lag_behind_master"
       in DBIx::Class::Storage::DBI method.  The default is 0.  In general, this should return a
       larger number when the replicant is lagging behind its master, however the implementation
       of this is database specific, so don't count on this number having a fixed meaning.  For
       example, MySQL will return a number of seconds that the replicating database is lagging.

   last_validated
       This is an integer representing a time since the last time the replicants were validated.
       It's nothing fancy, just an integer provided via the perl time built-in.

   replicant_type ($classname)
       Base class used to instantiate replicants that are in the pool.  Unless you need to
       subclass DBIx::Class::Storage::DBI::Replicated::Replicant you should just leave this
       alone.

   replicants
       A hashref of replicant, with the key being the dsn and the value returning the actual
       replicant storage.  For example, if the $dsn element is something like:

         "dbi:SQLite:dbname=dbfile"

       You could access the specific replicant via:

         $schema->storage->replicants->{'dbname=dbfile'}

       This attributes also supports the following helper methods:

       set_replicant($key=>$storage)
           Pushes a replicant onto the HashRef under $key

       get_replicant($key)
           Retrieves the named replicant

       has_replicants
           Returns true if the Pool defines replicants.

       num_replicants
           The number of replicants in the pool

       delete_replicant ($key)
           Removes the replicant under $key from the pool

   master
       Reference to the master Storage.

METHODS

       This class defines the following methods.

   connect_replicants ($schema, Array[$connect_info])
       Given an array of $dsn or connect_info structures suitable for connected to a database,
       create an DBIx::Class::Storage::DBI::Replicated::Replicant object and store it in the
       "replicants" attribute.

   connect_replicant ($schema, $connect_info)
       Given a schema object and a hashref of $connect_info, connect the replicant and return it.

   _safely_ensure_connected ($replicant)
       The standard ensure_connected method with throw an exception should it fail to connect.
       For the master database this is desirable, but since replicants are allowed to fail, this
       behavior is not desirable.  This method wraps the call to ensure_connected in an eval in
       order to catch any generated errors.  That way a slave can go completely offline (e.g. the
       box itself can die) without bringing down your entire pool of databases.

   _safely ($replicant, $name, $code)
       Execute $code for operation $name catching any exceptions and printing an error message to
       the "<$replicant-"debugobj>>.

       Returns 1 on success and undef on failure.

   connected_replicants
       Returns true if there are connected replicants.  Actually is overloaded to return the
       number of replicants.  So you can do stuff like:

         if( my $num_connected = $storage->has_connected_replicants ) {
           print "I have $num_connected connected replicants";
         } else {
           print "Sorry, no replicants.";
         }

       This method will actually test that each replicant in the "replicants" hashref is actually
       connected, try not to hit this 10 times a second.

   active_replicants
       This is an array of replicants that are considered to be active in the pool.  This does
       not check to see if they are connected, but if they are not, DBIC should automatically
       reconnect them for us when we hit them with a query.

   all_replicants
       Just a simple array of all the replicant storages.  No particular order to the array is
       given, nor should any meaning be derived.

   validate_replicants
       This does a check to see if 1) each replicate is connected (or reconnectable), 2) that is
       ->is_replicating, and 3) that it is not exceeding the lag amount defined by "maximum_lag".
       Replicants that fail any of these tests are set to inactive, and thus removed from the
       replication pool.

       This tests "all_replicants", since a replicant that has been previous marked as inactive
       can be reactivated should it start to pass the validation tests again.

       See DBIx::Class::Storage::DBI for more about checking if a replicating connection is not
       following a master or is lagging.

       Calling this method will generate queries on the replicant databases so it is not
       recommended that you run them very often.

       This method requires that your underlying storage engine supports some sort of native
       replication mechanism.  Currently only MySQL native replication is supported.  Your
       patches to make other replication types work are welcomed.

AUTHOR

       John Napiorkowski <john.napiorkowski@takkle.com>

LICENSE

       You may distribute this code under the same terms as Perl itself.

perl v5.18.1                                2013-DBIx::Class::Storage::DBI::Replicated::Pool(3pm)