PQL parsing of or clauses can exhaust memory

[rbrw]

It looks like the current PQL parser, using instaparse, consumes exorbitant quantities of RAM when attempting to parse or clauses. In a recent test instance with 1G allocated to puppetdb's heap, this query was enough to exhaust the heap in ~3m:

reports {
  latest_report? = true and (
    certname = "foo22" or
    certname = "foo21" or
    certname = "foo20" or
    certname = "foo19" or
    certname = "foo18" or
    certname = "foo17" or
    certname = "foo16" or
    certname = "foo15" or
    certname = "foo14" or
    certname = "foo13" or
    certname = "foo12" or
    certname = "foo11" or
    certname = "foo10" or
    certname = "foo9" or
    certname = "foo8" or
    certname = "foo7" or
    certname = "foo6" or
    certname = "foo5" or
    certname = "foo4" or
    certname = "foo3" or
    certname = "foo2" or
    certname = "foo1"
  )
}

Calling it with 21 OR clauses, the query succeeded in 31s, with 20 in 7s, with 19 in 4s, and so on back down to <1 once you reach 16 clauses.

As a temporary measure, use in instead of a set of ors; or wrap the ors in parentheses, although in general an in will be faster on the postgres side once the query's been parsed and postgres is actually running it.

[rbrw]

Fixed by c5e1f88