Before this commit, postgres would choose a non-optimal query
plan to find all presence rows belonging to a realm. We now
do an extra query to get the list of relevant user_ids, which allows
the next query to take advantage of UserPresence's index on
user_profile_id.
Here is the query plan for the offending query (this particular query isn't
verbatim from the code, but it's representative of the problem):
explain analyze
select client_id
from zerver_userpresence
INNER JOIN zerver_userprofile ON
zerver_userprofile.id = zerver_userpresence.user_profile_id
WHERE
zerver_userprofile.is_active and
zerver_userprofile.realm_id = 3;
Hash Join (cost=149.66..506.82 rows=5007 width=4) (actual time=48.834..121.215 rows=5007 loops=1)
Hash Cond: (zerver_userprofile.id = zerver_userpresence.user_profile_id)
-> Seq Scan on zerver_userprofile (cost=0.00..260.11 rows=5369 width=4) (actual time=0.009..24.322 rows=5021 loops=1)
Filter: (is_active AND (realm_id = 3))
Rows Removed by Filter: 3
-> Hash (cost=87.07..87.07 rows=5007 width=8) (actual time=48.789..48.789 rows=5010 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 196kB
-> Seq Scan on zerver_userpresence (cost=0.00..87.07 rows=5007 width=8) (actual time=0.007..24.355 rows=5010 loops=1)
Total runtime: 145.063 ms
You can see above that we're filtering on realm_id instead of using an index.
When you decompose the query into two queries, the total time is about 100ms, for a
savings of 33%. I imagine the savings would be even greater on an instance with lots
of realms. This was tested on dev with one really large realm and one tiny realm.
We were using `.order_by('user_profile_id', '-timestamp') in our
UserPresence query in get_status_dicts_for_query.
We don't need a full sort to produce the dictionary of statuses.
In fact the whole operation in Python is still O(N):
- divvy rows up to be per-user in an O(N) pass
- find max row for the 'aggregated' entry in an O(n) pass
per user
The one minor annoyance of this fix is that datetime_to_timestamp
is lossy, so if you naively call to_presence_dict before finding
the "max" row, you get test flakes if rows are created during the
same second. I decided to avoid calling to_presence_dict so there
are fewer moving parts, but there's still the ugly step of having
to remove the "dt" field from the final results.
The commit() call in fix() breaks migrations and tests (unless you
mock) due to outer transactions.
We now explicitly call commit() from the management command.
Usually a small minority of users are eligible to receive missed
message emails or mobile notifications.
We now filter users first before hitting UserPresence to find idle
users. We also simply check for the existence of recent activity
rather than borrowing the more complicated data structures that we
use for the buddy list.
Use jQuery DOM construction methods, rather than string concatenation,
to keep things structured and to stay clear of the lint rules introduced
in ee6235d71.
Until we get search bubbles, the search text is kind of a
distracting detail for most users. This just makes the
height 2px smaller for now. This will also make more text
show up on mobile web.
Travis enables different Python versions through virtual environments,
but it seems that there is a little caveat when we try to create Zulip's
virtual environment by referring Travis' virtual environment; Zulip's
virtual environment refers the system Python. We encountered this
behaviour when we tried to run our backend test suite under Python 3.5
in Travis. 'python3 --version' command before activating Zulip's
virtualenv showed 'Python 3.5.3' and after it showed 'Python 3.4.3'.
This happened when we created the virtual environment using
'virtualenv -p python3'.
The solution seems to be to explicitly give the path of the Python
interpreter in the Travis' virtual environment using 'which python3'.
This adds snakeviz to dev tools and also updates the message displayed
upon running `test-backend` with `--profile` option to say how to run
snakeviz correctly when using vagrant development environment.
If we use string concatenation to span i18n strings across multiple
lines then we end with such strings to be translated by the translators:
```
"This is the first line"\n + "This is the second line"
```
Steve Howell
Cynthia Lin
Akash Nimare
Brock Whittaker
Tommy Ip
Robert Hönig
Greg Price
Umair Khan
Aditya Bansal
Shubham Dhama