Replace the unused GIN index with a BTREE index

[SvetlinZarev]

Replace the unused GIN index with a BTREE index when searching by price, because the -> operator is not accelerated by the GIN index.

Each index in PG supports only specific "operator classes" (see https://www.postgresql.org/docs/current/gin.html#GIN-BUILTIN-OPCLASSES) . When working with JSONB, GIN has two modes:

• jsonb_ops (default), which supports the ?, ?|, ?&``@>, @?,@@,, etc operators
• jsonb_path_ops, which is smaller and faster, but supports only @>, @? and @@

Notice that none of those support ->, which means that the GIN index will not be used when filtering by jsonb -> 'price'. The gin is great only for "contains" type of operations.

In order to fix that, I replace the GIN, which indexes the whole JSON body, with a BTREE, which indexes only the property we are interested in. This should improve insterts/updates/deletes, as the index is smaller and faster to create/update. Also it will speed-up searches, because now the query will use the index to filter by price.

[antonputra]

Thank you @SvetlinZarev, I realized only after I ran this test. Good catch!