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WAIT FOR EVENT

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, SUBSCRIBE SET(7)). WAIT FOR EVENT may be used to cause the slonik script to wait until 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. The default value is 1.

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

ODDITIES

Not all events return interesting results. For instance, many people have run afoul of problems with SUBSCRIBE SET(7), when subscribing a new set. Be aware (and beware!) that a 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 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 SUBSCRIBE SET(7) is complete, you may submit a SYNC(7) event after the subscription, and have the WAIT request wait on that SYNC event, as follows.

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

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