bionic (7) SLONIK_WAIT_FOR_EVENT.7.gz

NAME

       WAIT FOR EVENT - Have Slonik script wait for previous event to complete

SYNOPSIS

       WAIT FOR EVENT (options);

DESCRIPTION

       Waits for event Confirmation.

       Slonik  remembers  the  last  event  generated on every node during script execution (events generated by
       earlier calls are currently not checked). In certain situations it is necessary that events generated  on
       one  node  (such as CREATE SET) are processed on another node before issuing more commands (for instance,
       SLONIK SUBSCRIBE SET(7)). WAIT FOR EVENT may be used to cause the slonik script to wait for  confirmation
       of an event, which hopefully means that the subscriber node is ready for the next action.

       WAIT FOR EVENT must be called outside of any try block in order to work, since new confirm messages don't
       become visible within a transaction.

       ORIGIN = ival | ALL
              The origin of the event(s) to wait for.

       CONFIRMED = ival | ALL
              The node ID of the receiver that must confirm the event(s).

       WAIT ON = ival
              The ID of the node where the “sl_confirm” [not available as a man page] table is to be checked.

       TIMEOUT = ival
              The number of seconds to wait. Default is 600 (10 minutes). TIMEOUT = 0 causes the script to  wait
              indefinitely.

EXAMPLE

       WAIT FOR EVENT (
         ORIGIN = ALL,
         CONFIRMED = ALL,
         WAIT ON = 1
       );

LOCKING BEHAVIOUR

       No application-visible locking should take place.

VERSION INFORMATION

       This command was introduced in Slony-I 1.0

       In version 2.0, the default value for WAIT ON was removed, so a node must be specified.

ODDITIES

       Not  all  events  return  interesting  results. For instance, many people have run afoul of problems with
       SLONIK SUBSCRIBE SET(7), when subscribing a new set. Be aware  (and  beware!)  that  a  SLONIK  SUBSCRIBE
       SET(7)  request will return the event confirmation almost immediately, even though there might be several
       hours of work to do before the subscription is ready. The trouble with SLONIK SUBSCRIBE SET(7) is that it
       is  processed  as two events, one on the origin node, with a second event, to enable the subscription, on
       the subscriber.

       In order to more reliably monitor from  within  a  slonik(1)  script  that  SLONIK  SUBSCRIBE  SET(7)  is
       complete, you may submit a SLONIK SYNC(7) event after the subscription, and have the WAIT request wait on
       the SYNC event, as follows.

            # Assuming that node 1 is the origin for set 999 that has direct subscribers 2 and 3
            SUBSCRIBE SET (ID = 999, PROVIDER = 1, RECEIVER = 2);
            WAIT FOR EVENT (ORIGIN = 1, CONFIRMED = ALL, WAIT ON=1);
            SUBSCRIBE SET (ID = 999, PROVIDER = 1, RECEIVER = 3);
            WAIT FOR EVENT (ORIGIN = 1, CONFIRMED = ALL, WAIT ON=1);
            MERGE SET ( ID = 1, ADD ID = 999, ORIGIN = 1 );

                                                21 September 2017                       SLONIK WAIT FOR EVENT(7)