Avoid Whoosh LockErrors

[jmonnich]

Whoosh only allows one writer at a time so opening another one fails with a LockError. This is bad UX since users might get an error when trying to create an event if the index is locked.

Using Whoosh's AsyncWriter would most likely solve this.

[pferreir]

As we've seen, AsyncWriter creates concurrency problems.
This is why we should use PostgreSQL's text search capabilities.

[iliastrichopoulos]

Code: ​https://github.com/nop33/indico/tree/move-to-psql-index

Testing the DB migration file:

indico db downgrade
indico db upgrade

The above commands work fine and they drop/create the DB structure as expected.

Importing data using

bin/migration/migrate.py

by running

python bin/migration/migrate.py --run-only reindexCategoryNameAndConferenceTitle --prev-version 1.8

Creating / Renaming / Deleting Categories and Events is updating the index tables correctly.
Searching for Events using the HTTP API gives correct results.

Could not find HTTP API method to search for Categories, so I tried it from the indico shell and it worked fine.

[iliastrichopoulos]

Need to be tested in indico-build. After that it'll be ready to merge.