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new bb5dbe3 Ignite docs: added the note about continuous queries
exactly-once guarantee.
new 9e18e07 Merge remote-tracking branch 'origin/master'
bb5dbe3 is described below
commit bb5dbe3c4a951bddd17f2ab9094ddd69b1779cee
Author: Denis Magda <dma...@gridgain.com>
AuthorDate: Tue Oct 6 16:02:56 2020 -0700
Ignite docs: added the note about continuous queries exactly-once guarantee.
---
docs/_docs/key-value-api/continuous-queries.adoc | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/docs/_docs/key-value-api/continuous-queries.adoc
b/docs/_docs/key-value-api/continuous-queries.adoc
index 8f90dbdb..73343d3 100644
--- a/docs/_docs/key-value-api/continuous-queries.adoc
+++ b/docs/_docs/key-value-api/continuous-queries.adoc
@@ -136,6 +136,21 @@ You can do this in two ways:
* link:code-deployment/peer-class-loading[Enable peer class loading].
====
+== Events Delivery Guarantees
+
+Continuous queries ensure the exactly-once semantic for the delivery of events
to the clients' local listeners.
+
+Both primary and backup nodes maintain an update queue that holds events that
are processed by continuous queries
+on the server side but yet to be delivered to the clients. Suppose a primary
node crashes
+or the cluster topology changes for any reason. In that case, every backup
node flushes the content of its update
+queue to the client, making sure that every event is delivered to the client's
local listener.
+
+Ignite manages a special per-partition update counter that helps to avoid
duplicate notifications. Once an entry in
+some partition is updated, a counter for this partition is incremented on both
primary and backup nodes. The value of
+this counter is also sent along with the event notification to the client.
Thus, the client can skip already-processed
+events. Once the client confirms that an event is received, the primary and
backup nodes remove the record for this event
+from their backup queues.
+
== Examples
