On Mon, Jul 8 2024 at 08:51:58 PM +00:00:00, Zbigniew
Jędrzejewski-Szmek <zbyszek@xxxxxxxxx> wrote:
Does the table store counts or separate entries? I would guess that if
it just stores disaggregated values, then the values repeat often, and
it's natural to store the count in the table. And then the order
doesn't matter, because it'll be different in different tables.
It stores separate entries (disaggregated). For some metrics, the
values will repeat often. For others, they won't. For example:
azafea=# SELECT * FROM daily_session_time_v3;
id | os_version | period_start | count |
channel_id
-----+-------------------------------------+--------------+-------+------------
1 | 38 (Workstation Edition Prerelease) | 2023-03-23 | 31975 |
1
2 | 38 (Workstation Edition Prerelease) | 2023-03-24 | 35993 |
1
3 | 38 (Workstation Edition Prerelease) | 2023-03-25 | 6431 |
1
4 | 38 (Workstation Edition Prerelease) | 2023-03-26 | 8203 |
1
Here it so happens that I am the only user (so now you know I spend
much less time on my computer on weekends); in a real deployment there
would of course be a huge number of daily events. But now say
hypothetically that another unrelated event also occurs when the user
session begins and gets stored into a different table. Then if we don't
shuffle the table rows, you could infer that the same user submitted
metrics to the two separate tables just by the order of the rows.
Probably not a big deal since none of the data we collect should be
identifiable, but I've promised that aggregating the data is not
supposed to be possible, so got to solve that somehow. Shuffling is the
easy solution.
(Note this particular daily_session_time_v3 record is just an example
of data that Endless collects. I'm *not* proposing that Fedora should
collect this particular data. It probably wouldn't be useful for us. We
decide what we collect.)
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