This is so that we correctly order _a_history later.

This doesn't work with locks yet.

Read in backend works now, insert and upsert not yet.

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E[wrixteecNSotdaetSutso r=i eFsa]t a[l(E)r]r
or, sqlErrorMsg = "une instruction insert ou update sur la table \194\171 context_node_ngrams \194\187 viole la contrainte de cl\195\169\n\195\169trang\195\168re \194\171 context_node_ngrams_context_id_fkey \194\187", sqlErrorDetail = "La cl\195\169 (context_id)=(135) n'est pas pr\195\169sente dans la table \194\171 nodes \194\187.", sqlErrorHint = ""}

[TOOLING] sql queries to remove unused documents and ngrams from database. Usage: use a crontab to execute it every week for instance.

Also, pin postgres to v11 so that we're compatible with Debian
upstream.

This caused subtle bugs when ALTER TABLE with search_title was
called. It is a wrong practice to define an index immutable when in
fact it's not. The count(id) part makes it mutable in fact.

This reverts commit 29ee1972.

It introduces a bug, it should not be merged.

However, the code doesn't work currently.

This has couple of drawbacks:
- we use postgres-simple and a raw sql query, opaleye would be better
I guess
- there is a hack for empty query, this should be replaced by
removing the WHERE clause in this case