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.

FURTHER QUESTIONS?

       Check the list of additional DBIC resources.

COPYRIGHT AND LICENSE

       This module is free software copyright by the DBIx::Class (DBIC) authors. You can redistribute it  and/or
       modify it under the same terms as the DBIx::Class library.

perl v5.40.0                                       2025-02-01              DBIx::Class::S...eplicated::Pool(3pm)