nlargest is the natural fit for selecting n biggest items
from an unsorted list. It's more readable as well as more
efficent (even though we don't care much about the efficeny
in this particular case).
This makes us more efficient when handling
multiple users. We don't have to keep
sending the same two queries to the database.
Note that as part of this we eliminated
a failure mode for the obscure population
of users from whom both `user.is_guest` and
`user.can_access_public_streams()` returns
False. We know this would have only affected
Zephyr users (by looking at the code), and
we know we don't actually process Zephyr
users for email digests (or else we would
have raised exceptions in the old code).
We mostly need realm_id, but when we go to build
message lists, we need realm.uri.
We could probably be more aggresive about using
`only` here, but for now I am just trying to
reduce hops to the database.
Note that we are much more efficient about finding
active users here:
- we do one query per realm (instead of per-user)
- we pass the cutoff date to the database
- we get back just a list of distinct ids
This function is going away completely soon. It is
querying everybody's entire UserActivity history instead
of passing the cutoff date to the database!
The query counts increase here for somewhat
contrived reasons. The tests before this
commit reflected a successful trip to the
UserProfile cache, but that's not actually
realistic in practice.
The code we deleted here was no longer
doing anything.
Maybe the code was always dead, or maybe it
was written during a time when topics_by_diversity
and topics_by_length actually had different keys.
But now it's clearly cruft.
If we have 4 or more topics, then the code above
it would already have populated the list with 4
elements, and the `if num_convos < 4` condition
would evaluate to False.
And if we had 3 or fewer topics, then we would
have already put all possible topics into our
result, and the `topics_by_diversity[num_convos:4]`
slice would be empty.
It's possible that we should just have a simple
heuristic for topic hotness like `10*num_senders
+ messages`, so we don't have to maintain this
fiddly function, and we can just do something like
`topics_by_score[:4]`.
I now use sets for stream_ids in more of the digest
code.
As part of this I replaced exclude_subscription_modified_streams
with streams_recently_modified_for_user.
It's easier for the caller to just ask for ids
to delete from its callee than it is to pass
in a set/list to mutate.
The simpler boundary between the functions makes
the tests easier to write--you can see the
`filtered_streams` logic goes away in this diff.
I also make the tests a bit more thorough by using
combinations of Cordelia/Othello and Verona/Denmark
to try to find multiple possible flaws.
And I make the time intervals longer than 1s to
avoid false negatives from slow CI boxes.
If we have multiple users, this reduces the amount
of queries we need to do, because we get all
subscriptions for all users in a single query
to Subscription.
For the single-user case, we are introducing an
extra query hop, but the database is doing
roughly the same work, because we are just breaking
up this complex query into two hops:
messages =
select ... from message
where recipient__type_id in (
select stream_id from subscription
where ...
)
Now it's more like:
stream_ids =
select stream_id from subscription
where ...
messages =
select ... from message
where recipient__type_id in stream_ids
Note that we are not changing anything semantically
or algorithmically yet. The only overhead here
for the single-user case is boxing and unboxing
data into single-item dicts and lists.
The interfaces for callers in the view and the
queue processor remain the same for now.
This extraction will make a bit more sense when
we start doing bulk operations on a realm to
get digests, but even now, it encapsulates the
slightly complex way we cherry-pick the top 4
topics for a user.
This prep step is mostly for diff hygiene; the next
commit will make the code a bit nicer.
The original code here had the nice property that
most (but not all) of the DB work happened up
front in `handle_digest_email`, and none of the
DB work was delegated to the callers. But I
prefer the tradeoff of making the helpers a bit
more cohesive--let them get the data they need.
And we have query-count coverage in our tests,
so there's no real danger of having helpers
down in the stack insidiously doing a bunch of
extra DB hops.
This reverts commit c3779338c6 (part
of #14638), which incorrectly depended on commits from the future,
with the effect of either halting the flow of entropic time in an
irresolvable temporal paradox, summoning extradimensional beings to
rain destruction on the galaxy, or failing CI.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Anders Kaseorg
Vishnu KS
Alex Vandiver
Tim Abbott
Steve Howell
Clara Dantas