This commit introduces the ability to do custom fetches
and to essentially use temp tables for intermediate results.
(The temp table stuff deals with recipients/subscriptions
having three different flavors--user, stream, and huddle.)
The function to create the message partial files has been
renamed to export_partial_message_files(). It now gets its own
list of user profile ids and recipient ids from the response,
so that we can de-clutter do_export_realm().
The name avatar_bucket was confusing for a boolean, and
in some places it was used for non-S3 paths.
I considered the more concise 'is_avatar', but that
was still confusing when you are processing multiple
files, because you think it's a calculated property
on one file instead of an overall codepath switch.
I also considered splitting up some functions, but
there is a lot of common logic between handling
file uploads and avatars that's not trivial to extract
into helpers, especially on the S3 side.
I did some minor moving around of code that made us have
one fewer function without any additional conditional
logic. The names are more explicit about saying
"from_local" and "from_s3". Also, there is less clutter
now in do_export_realm(), which is evolving into more of
a dispatcher and less of a worker.
This is pretty minor cleanup, but it makes it a little more
explicit what we're writing to the shard file, and it allows
us to use a more specific mypy type when calling
floatify_datetime_fields.
We no longer have an in-process code path to export
UserMessage rows. We want to only maintain the
subprocess code, which we'll always use in production,
and which will work fine in dev.
I also fixed some small things like removing unnecessary return
statements, and adding a TODO.
In some cases I explicitly cast stuff at run-time to set() or
str() to appease mypy, as well as make it clear to somebody
reading the code that the callee might not respect ordering
or tolerate unicode.
The previous export tool would only work properly for small realms,
and was missing a number of important features:
* Export of avatars and uploads from S3
* Export of presence data, activity data, etc.
* Faithful export/import of timestamps
* Parallel export of messages
* Not OOM killing for large realms
The new tool runs as a pair of documented management commands, and
solves all of those problems.
Also we add a new management command for exporting the data of an
individual user.
Steve Howell
Tim Abbott