Remove functionality associated with unused historical stats tables (#9721)

Fixes #9602

1 files changed, 5 insertions, 45 deletions

diff --git a/docs/room_and_user_statistics.md b/docs/room_and_user_statistics.md
index e1facb38d4..cc38c890bb 100644
--- a/docs/room_and_user_statistics.md
+++ b/docs/room_and_user_statistics.md
@@ -1,9 +1,9 @@
 Room and User Statistics
 ========================
 
-Synapse maintains room and user statistics (as well as a cache of room state),
-in various tables. These can be used for administrative purposes but are also
-used when generating the public room directory.
+Synapse maintains room and user statistics in various tables. These can be used
+for administrative purposes but are also used when generating the public room
+directory.
 
 
 # Synapse Developer Documentation
@@ -15,48 +15,8 @@ used when generating the public room directory.
 * **subject**: Something we are tracking stats about – currently a room or user.
 * **current row**: An entry for a subject in the appropriate current statistics
     table. Each subject can have only one.
-* **historical row**: An entry for a subject in the appropriate historical
-    statistics table. Each subject can have any number of these.
 
 ### Overview
 
-Stats are maintained as time series. There are two kinds of column:
-
-* absolute columns – where the value is correct for the time given by `end_ts`
-    in the stats row. (Imagine a line graph for these values)
-    * They can also be thought of as 'gauges' in Prometheus, if you are familiar.
-* per-slice columns – where the value corresponds to how many of the occurrences
-    occurred within the time slice given by `(end_ts − bucket_size)…end_ts`
-    or `start_ts…end_ts`. (Imagine a histogram for these values)
-
-Stats are maintained in two tables (for each type): current and historical.
-
-Current stats correspond to the present values. Each subject can only have one
-entry.
-
-Historical stats correspond to values in the past. Subjects may have multiple
-entries.
-
-## Concepts around the management of stats
-
-### Current rows
-
-Current rows contain the most up-to-date statistics for a room.
-They only contain absolute columns
-
-### Historical rows
-
-Historical rows can always be considered to be valid for the time slice and
-end time specified.
-
-* historical rows will not exist for every time slice – they will be omitted
-    if there were no changes. In this case, the following assumptions can be
-    made to interpolate/recreate missing rows:
-    - absolute fields have the same values as in the preceding row
-    - per-slice fields are zero (`0`)
-* historical rows will not be retained forever – rows older than a configurable
-    time will be purged.
-
-#### Purge
-
-The purging of historical rows is not yet implemented.
+Stats correspond to the present values. Current rows contain the most up-to-date
+statistics for a room. Each subject can only have one entry.