Performance issue with self-assign dashboard

[torgeirl]

There seems to be a performance issue with the self-assign dashboard (#1218). According to Google Chrome's performance insights, the HTML has a waiting time of above 5s while the download time is ~zero. This could be related to #1236.

Edit: it might be an issue with how the filter(s) are build, I get terrible preformance for /devilry_examiner/self-assign/<semester-code>/filter/assignedstatus-assigned?cradmin-bgreplaced=true especially.

[espenak]

@torgeirl: As far as I can tell this must be because of the "count" queries that is used to filter by status and to show the counts in the status filters. We CAN change this to use much cheaper exists queries, but then we can not show the counts in the status filter.

It should really not be a problem to handle counts of a few thousand - we normally see this problem when counting millions or at least hundreds of thousands. The problem is usually that postgres has:

• To little disk space (it really likes a lot of disk space to get good IOPS because it caches data is many different ways if it can.
• Too little memory - if the indexes do not fit in memory, things slow down.

[torgeirl]

The problem is usually that postgres has:

• To little disk space (it really likes a lot of disk space to get good IOPS because it caches data is many different ways if it can.
• Too little memory - if the indexes do not fit in memory, things slow down.

@espenak: I'm checking disk and memory status now to rule that out.

[torgeirl]

@espenak: our database server is plentiful on both disk space and memory; in fact, its postgres cache is about the same size of the entire database including indexes.

[torgeirl]

it might be an issue with how the filter(s) are build, I get terrible preformance for /devilry_examiner/self-assign/<semester-code>/filter/assignedstatus-assigned?cradmin-bgreplaced=true especially.

Transactions for /devilry_examiner/self-assign/{roleid}/filter/{filters_string} can be another place to look. Especially two of the 15 DB look-ups invoked by the view render for devilry_examiner_selfassign-self-assign-filter take up to 300-400s each, causing the transaction taking a total of 2s.