randgen: add PopulateTableWithRandData

[msbutler]

PopulateTableWithRandData populates the caller's table with random data. This helper
function aims to make it easier for engineers to develop randomized tests that
leverage randgen / sqlsmith.

Informs #72345

Release note: None

[cockroach-teamcity]

This change is 

[stevendanna]

Looks useful! Just some drive-by comments.

[mgartner]

Reviewed 4 of 6 files at r2, 3 of 3 files at r3, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @msbutler and @stevendanna)

---

bazel-out, line 1 at r3 (raw file):

/private/var/tmp/_bazel_michaelbutler/13ba282fa2b19539d0c969c1113bb37c/execroot/cockroach/bazel-out

Is this file necessary, or did you commit it by error?

---

pkg/sql/randgen/schema.go, line 221 at r3 (raw file):

		if colTypes[j].Family() == types.OidFamily {
			// choose 0 or 1 as the OID value as the value must be less than the
			// number of tables in the database.

As far as I can tell, there is only a limit on REGTYPE, not any other types in the OID family (OID, REGCLASS, REGPROC, REGPROCEDURE, REGROLE, REGNAMESPACE).

---

pkg/sql/randgen/schema.go, line 231 at r3 (raw file):

	}
	valBuilder.WriteString(")")
	return valBuilder

nit: might as well return a string instead of the builder

---

pkg/sql/randgen/schema.go, line 237 at r3 (raw file):

func PopulateTableWithRandData(rng *rand.Rand, db *gosql.DB, tableName string, numRows int) error {
	var ignored, createStmtSQL string
	res := db.QueryRow(fmt.Sprintf("SHOW CREATE TABLE %s", tableName))

nit: You don't need ignored if you change the query to SELECT create_statement FROM [SHOW CREATE TABLE %].

---

pkg/sql/randgen/schema.go, line 284 at r3 (raw file):

			} else {
				nullable = append(nullable, false)
			}

nit: this can be simplified to nullable = append(nullable col.Nullable.Nullability == tree.Null).

---

pkg/sql/randgen/schema.go, line 295 at r3 (raw file):

		fail    int // number of failed insert statements
	)
	maxTries := numRows * 10

I'm a little worried that trying only 10 times per row will cause the tests to flake. Have you tried stressing the test to see how likely it is to fail?

---

pkg/sql/randgen/schema.go, line 309 at r3 (raw file):

			if fail > maxTries {
				// This could mean PopulateTableWithRandomData or RandDatum couldn't
				// handle this table's schema. consider filing a bug.

nit: consider => Consider

---

pkg/sql/randgen/schema.go, line 310 at r3 (raw file):

				// This could mean PopulateTableWithRandomData or RandDatum couldn't
				// handle this table's schema. consider filing a bug.
				return errors.Errorf(`could not populate %d rows for table with schema \n \t %s \n--

This function isn't being used yet, so I'm not sure what the usage pattern will be, but I'm wondering if it would make more sense to return no error in this case. Perhaps a better API would be something like:

func PopulateTableWithRandData(
    rng *rand.Rand,
    db *gosql.DB,
    tableName string,
    numInserts int,
) (numRowsInserted int, err error)

The function would attempt exactly numInserts INSERT statements, none of which are guaranteed to succeed. It would return the number of rows successfully inserted. An error is returned if no inserts could be attempted (the table doesn't exist, or the create statement failed to parse). I think this would make the behavior of this function more predictable and let callers decide how many inserts they want to perform and how to proceed given the number of successfully inserted rows.

[msbutler]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @mgartner and @stevendanna)

---

pkg/sql/randgen/schema.go, line 221 at r3 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

As far as I can tell, there is only a limit on REGTYPE, not any other types in the OID family (OID, REGCLASS, REGPROC, REGPROCEDURE, REGROLE, REGNAMESPACE).

Done.

---

pkg/sql/randgen/schema.go, line 295 at r3 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

I'm a little worried that trying only 10 times per row will cause the tests to flake. Have you tried stressing the test to see how likely it is to fail?

I got it to pass the stress test a few times with a multiplier of 10, though I'll bump it to 100. In a previous iteration of this test, I was hitting OOM errors on the stress test, which compelled me to lower the multiplier, but a lot has changed since I was OOMing.

---

pkg/sql/randgen/schema.go, line 310 at r3 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

This function isn't being used yet, so I'm not sure what the usage pattern will be, but I'm wondering if it would make more sense to return no error in this case. Perhaps a better API would be something like:

func PopulateTableWithRandData(
    rng *rand.Rand,
    db *gosql.DB,
    tableName string,
    numInserts int,
) (numRowsInserted int, err error)

The function would attempt exactly numInserts INSERT statements, none of which are guaranteed to succeed. It would return the number of rows successfully inserted. An error is returned if no inserts could be attempted (the table doesn't exist, or the create statement failed to parse). I think this would make the behavior of this function more predictable and let callers decide how many inserts they want to perform and how to proceed given the number of successfully inserted rows.

I like this idea! Then, schema_test will pass if at least one of the 10 randomly generated tables had a numRowsInserted>0.

---

bazel-out, line 1 at r3 (raw file):

Previously, mgartner (Marcus Gartner) wrote…

Is this file necessary, or did you commit it by error?

whoops. removed.

[mgartner]

Reviewed 4 of 4 files at r4, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner and @stevendanna)

[msbutler]

TFTR!!!

bors r=mgartner

[craig]

Build failed:

• GitHub CI (Cockroach)

[msbutler]

bors r=mgartner

[craig]

Build succeeded:

• GitHub CI (Cockroach)