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authorErik Johnston <erikj@jki.re>2019-02-19 13:14:30 +0000
committerGitHub <noreply@github.com>2019-02-19 13:14:30 +0000
commitc003450057057106d4032a152eff931f4fc34f1c (patch)
tree57fb93ef20a0c5c02c1a13715e96514264daa5e7 /docs/tcp_replication.rst
parentMerge pull request #4676 from matrix-org/rav/pg95 (diff)
parentDocs (diff)
downloadsynapse-c003450057057106d4032a152eff931f4fc34f1c.tar.xz
Merge pull request #4671 from matrix-org/erikj/state_cache_invalidation
Batch cache invalidation over replication
Diffstat (limited to 'docs/tcp_replication.rst')
-rw-r--r--docs/tcp_replication.rst26
1 files changed, 25 insertions, 1 deletions
diff --git a/docs/tcp_replication.rst b/docs/tcp_replication.rst
index 62225ba6f4..73436cea62 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 +220,28 @@ 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.
+
+Currently the special cache names are declared in ``synapse/storage/_base.py``
+and are:
+
+1. ``cs_cache_fake`` ─ invalidates caches that depend on the current state