builtins,workload: add setseed function; use it to make RSW more deterministic

[rafiss]

This implements the setseed function that appears in PostgreSQL.

We then use it to make the ORDER BY random()
clauses used in the random schema workload (RSW) deterministic.

Each worker goroutine of the RSW now runs a determistic sequence of
operations given the same COCKROACH_RANDOM_SEED. However, since the
workload is concurrent, the overall RSW is not deterministic, since the
interleaving of goroutine execution is random.

informs #117422

Release note (sql change): Added the setseed() builtin function. It sets
the seed for the random generator used by the random() builtin function.

[cockroach-teamcity]

This change is 

[fqazi]

Nice work and this vastly improves things!

Reviewed 12 of 12 files at r1, 2 of 2 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @annrpom, @rafiss, @renatolabs, and @srosenberg)

---

pkg/workload/schemachange/operation_generator.go line 3259 at r2 (raw file):

	ctx context.Context, tx pgx.Tx, tableName tree.TableName, pctExisting int,
) (string, error) {
	if err := og.setSeedInDB(ctx, tx); err != nil {

Would it make sense for the worker to some how just do this once? I think that doesn't work because we can have expressions with random I think.

[rafiss]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @annrpom, @fqazi, @renatolabs, and @srosenberg)

---

pkg/workload/schemachange/operation_generator.go line 3259 at r2 (raw file):

Previously, fqazi (Faizan Qazi) wrote…

Would it make sense for the worker to some how just do this once? I think that doesn't work because we can have expressions with random I think.

i think it needs to be per-op, due to interleaving execution of goroutines fighting against determinism. here's an example to see why:

scenario 1:

goroutine 1: CREATE TABLE t;
goroutine 1: DROP TABLE t;
goroutine 2: CREATE VIEW AS ... -- requires picking a table by sorting by random()

scenario 2:

goroutine 1: CREATE TABLE t;
goroutine 2: CREATE VIEW AS ... -- requires picking a table by sorting by random()
goroutine 1: DROP TABLE t;

in the first scenario, goroutine 2 will have invoked random() 0 times, since there were no tables to sort. in the second scenario, goroutine 2 will have invoked random() once, since it found a table to use.

however, the next time goroutine 2 uses random() we want it to generate the same number in both scenarios.

[rafiss]

tftr!

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)