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authorErik Johnston <erik@matrix.org>2019-02-19 11:24:59 +0000
committerErik Johnston <erik@matrix.org>2019-02-19 11:24:59 +0000
commitbc8fa1509d3885d111a2ef98e12e9ce66a19a3a8 (patch)
tree8622c7dbfa599f0c9f2422020d0d505c51a59015 /docs/tcp_replication.rst
parentNewsfile (diff)
downloadsynapse-bc8fa1509d3885d111a2ef98e12e9ce66a19a3a8.tar.xz
Documentation
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diff --git a/docs/tcp_replication.rst b/docs/tcp_replication.rst
index 62225ba6f4..852f1113a3 100644
--- a/docs/tcp_replication.rst
+++ b/docs/tcp_replication.rst
@@ -137,7 +137,6 @@ for each stream so that on reconneciton it can start streaming from the correct
 place. Note: not all RDATA have valid tokens due to batching. See
 ``RdataCommand`` for more details.
 
-
 Example
 ~~~~~~~
 
@@ -221,3 +220,23 @@ SYNC (S, C)
 
 See ``synapse/replication/tcp/commands.py`` for a detailed description and the
 format of each command.
+
+
+Cache Invalidation Stream
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The cache invalidation stream is used to inform workers when they need to
+invalidate any of their caches in the data store. This is done by streaming all
+cache invalidations done on master down to the workers, assuming that any caches
+on the workers also exist on the master.
+
+Each individual cache invalidation results in a row being sent down replication,
+which includes the cache name (the name of the function) and they key to
+invalidate. For example::
+
+    > RDATA caches 550953771 ["get_user_by_id", ["@bob:example.com"], 1550574873251]
+
+However, there are times when a number of caches need to be invalidated at the
+same time with the same key. To reduce traffic we batch those invalidations into
+a single poke by defining a special cache name that workers understand to mean
+to expand to invalidate the correct caches.