From c8b12a3a3ad44bbd0ab33b19d4f799d063b780fa Mon Sep 17 00:00:00 2001
From: David Robertson <davidr@element.io>
Date: Wed, 20 Jul 2022 17:56:06 +0100
Subject: [PATCH 1/2] Track DB txn times w/ two counters, not histogram

By my reckoning, this should mean that each txn `desc` produces 2 time
series, down from 17. If we don't like this, we could keep the histogram
but configure it with coarser buckets.

Closes #11081.
---
 synapse/storage/database.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index ea672ff89e73..b394a6658b09 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -39,7 +39,7 @@
 )
 
 import attr
-from prometheus_client import Histogram
+from prometheus_client import Counter, Histogram
 from typing_extensions import Concatenate, Literal, ParamSpec
 
 from twisted.enterprise import adbapi
@@ -76,7 +76,8 @@
 sql_scheduling_timer = Histogram("synapse_storage_schedule_time", "sec")
 
 sql_query_timer = Histogram("synapse_storage_query_time", "sec", ["verb"])
-sql_txn_timer = Histogram("synapse_storage_transaction_time", "sec", ["desc"])
+sql_txn_count = Counter("synapse_storage_transaction_time_count", "sec", ["desc"])
+sql_txn_duration = Counter("synapse_storage_transaction_time_sum", "sec", ["desc"])
 
 
 # Unique indexes which have been added in background updates. Maps from table name
@@ -795,7 +796,8 @@ def new_transaction(
 
             self._current_txn_total_time += duration
             self._txn_perf_counters.update(desc, duration)
-            sql_txn_timer.labels(desc).observe(duration)
+            sql_txn_count.labels(desc).inc(1)
+            sql_txn_duration.labels(desc).inc(duration)
 
     async def runInteraction(
         self,

From 490af3af887720701222d83773176fc20f4f5216 Mon Sep 17 00:00:00 2001
From: David Robertson <davidr@element.io>
Date: Wed, 20 Jul 2022 18:24:02 +0100
Subject: [PATCH 2/2] Changelog

---
 changelog.d/13342.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/13342.misc

diff --git a/changelog.d/13342.misc b/changelog.d/13342.misc
new file mode 100644
index 000000000000..ce9c816b9c1a
--- /dev/null
+++ b/changelog.d/13342.misc
@@ -0,0 +1 @@
+When reporting metrics is enabled, use ~8x less data to describe DB transaction metrics.