use boolean for span value on plan gist

[maryliag]

Currently when creating the plan hash/plan gist, it uses the literal value on the span, and different values of span creates different plan gists. This is rapidly increasing the cardinality of rows on statement_statistics since a new row is created for each unique plan.

E.g.

root@localhost:26257/defaultdb> SELECT crdb_internal.decode_plan_gist('AgHIAQIAfg4AAAYM');
  crdb_internal.decode_plan_gist
----------------------------------
  • scan
    table: ?@?
    spans: 7 spans
(3 rows)

root@localhost:26257/defaultdb> SELECT crdb_internal.decode_plan_gist('AgHIAQIAfgIAAAYM');
  crdb_internal.decode_plan_gist
----------------------------------
  • scan
    table: ?@?
    spans: 1 span
(3 rows)

We would like the span value to be changed to a boolean instead, to follow the example of the limit, this way the same plan with different span values would all have the same hash/gist.

Context https://cockroachlabs.slack.com/archives/C01RX2G8LT1/p1661804175738409

Jira issue: CRDB-19170