Commit Graph

10 Commits

Author SHA1 Message Date
Erik Johnston
bd380d942f
Add checks for postgres sequence consistency (#8402) 2020-09-28 18:00:30 +01:00
Erik Johnston
f112cfe5bb
Fix MultiWriteIdGenerator's handling of restarts. (#8374)
On startup `MultiWriteIdGenerator` fetches the maximum stream ID for
each instance from the table and uses that as its initial "current
position" for each writer. This is problematic as a) it involves either
a scan of events table or an index (neither of which is ideal), and b)
if rows are being persisted out of order elsewhere while the process
restarts then using the maximum stream ID is not correct. This could
theoretically lead to race conditions where e.g. events that are
persisted out of order are not sent down sync streams.

We fix this by creating a new table that tracks the current positions of
each writer to the stream, and update it each time we finish persisting
a new entry. This is a relatively small overhead when persisting events.
However for the cache invalidation stream this is a much bigger relative
overhead, so instead we note that for invalidation we don't actually
care about reliability over restarts (as there's no caches to
invalidate) and simply don't bother reading and writing to the new table
in that particular case.
2020-09-24 16:53:51 +01:00
Erik Johnston
cbabb312e0
Use async with for ID gens (#8383)
This will allow us to hit the DB after we've finished using the generated stream ID.
2020-09-23 16:11:18 +01:00
Erik Johnston
deedb91732
Fix MultiWriterIdGenerator.current_position. (#8257)
It did not correctly handle IDs finishing being persisted out of
order, resulting in the `current_position` lagging until new IDs are
persisted.
2020-09-08 14:26:54 +01:00
Erik Johnston
bbb3c8641c
Make MultiWriterIDGenerator work for streams that use negative stream IDs (#8203)
This is so that we can use it for the backfill events stream.
2020-09-01 13:36:25 +01:00
Erik Johnston
5649b7f3d0
Fix missing _add_persisted_position (#8179)
This was forgotten in #8164.
2020-08-27 13:20:34 +01:00
Erik Johnston
eba98fb024
Add functions to MultiWriterIdGen used by events stream (#8164) 2020-08-25 17:32:30 +01:00
Erik Johnston
76d21d14a0
Separate get_current_token into two. (#8113)
The function is used for two purposes: 1) for subscribers of streams to
get a token they can use to get further updates with, and 2) for
replication to track position of the writers of the stream.

For streams with a single writer the two scenarios produce the same
result, however the situation becomes complicated for streams with
multiple writers. The current `MultiWriterIdGenerator` does not
correctly handle the first case (which is not an issue as its only used
for the `caches` stream which nothing subscribes to outside of
replication).
2020-08-19 10:39:31 +01:00
Erik Johnston
a7bdf98d01
Rename database classes to make some sense (#8033) 2020-08-05 21:38:57 +01:00
Erik Johnston
8123b2f909
Add MultiWriterIdGenerator. (#7281)
This will be used to coordinate stream IDs across multiple writers.

Functions as the equivalent of both `StreamIdGenerator` and
`SlavedIdTracker`.
2020-05-04 17:17:45 +01:00