make dashboard readPreference from secondary

[drorsun]

I would like to be able to configure parse-dashboard to prefer secondary replica-set members in mongo db when scanning for data. I understand this involves integration with the parse-server which is actually holding the connections and doing the queries, but is that somehow possible today?

If not please consider this a feature request.

[johanarnor]

@drorsun @flovilmart Any specific reason this was closed? I guess it's possible now, since parse-community/parse-server#3865 is merged? I can take a stab at a PR, if someone guides me in the right direction.

It would really help with #612 as well.

[flovilmart]

Closed due to inactivity and lack of interest.

I don’t know what the right direction is for this one.

Also it’s pretty much unrelated to the issues hou’re describing.

You’ll be trashing the secondary, which in turn will increase the replication lag, which in turn will trash the primary.

Possible solutions:

1. A dedicated server instance for your dashboard that writes all requests with secondary; and not the main one.
2. Properly index your data
3. Configure correctly the maxMs for mongo, so your queries don’t run indefinitely

[johanarnor]

First, sorry I didn't see that the PR was closed 2 years after opening. Just saw 26 Jun 2016 -> closed on 26 Jun and assumed it was the same year.

Hm, didn't know that thrashing the secondary would severely impact the primary.

Regarding the solutions:

1. Is it possible to write to the secondary DB as well? I assumed that one could only write to primary in order to not make the DBs out of sync.
2. It's quite wasteful to index every single "column", especially if we need 'createdAt' in the index as well.
3. Will take a look at the maxMs, thanks.