Enable PostgreSQL connection pooling

added part::backend label

@hansegucker Can you please test in your environment? Also, if this makes anything faster (thinking of SSL handshakes in PostgreSQL).

Caveat: Your PostgreSQL server must handle as many connections as your application server starts threads (i.e. processes * threads connections when using uWSGI).

Looks very fine in first tests. I will watch the behavior for the next day or so, but in general I think this can be merged.

added 23 commits

• 8c768bf6...ad80080e - 22 commits from branch master
• bbc4e336 - Merge branch 'master' into feature/connection_pooling

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assigned to @nik and unassigned @hansegucker

merged

mentioned in commit b775350f