Unique index is necessary when one wants to refresh the view
concurrently.

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.

[*r*epoSaver*A cEtxicoen]p "rtepioosn/:no deSqlError Id{-0s-tqmlp-Srteatepo1 2=3 8"22-3150013."c,b osrq"l
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.