sql, featureflag: add schema change feature flag

[angelapwen]

The following features have been tested and act as expected:

• ALTER DATABASE OWNER
• ALTER DATABASE ADD REGION
• ALTER DATABASE DROP REGION
• ALTER DATABASE SURVIVE
• ALTER TABLE REGIONAL AFFINITY
• ALTER TABLE SET SCHEMA
• ALTER SCHEMA
• ALTER TYPE
• ALTER SEQUENCE RENAME
• ALTER SEQUENCE SET SCHEMA
• CREATE DATABASE
• CREATE INDEX
• CREATE SCHEMA
• CREATE TABLE
• CREATE TYPE
• CREATE VIEW
• CREATE SEQUENCE
• DROP DATABASE
• DROP INDEX
• DROP TABLE
• DROP VIEW
• DROP SEQUENCE
• DROP TYPE
• DROP SCHEMA
• REASSIGN OWNED BY
• DROP OWNED BY
• RENAME DATABASE
• REPARENT DATABASE
• RENAME INDEX
• RENAME TABLE
• RENAME COLUMN
• COMMENT ON COLUMN
• COMMENT ON DATABASE
• COMMENT ON INDEX
• COMMENT ON TABLE
• ALTER INDEX CONFIGURE ZONE
• ALTER TABLE CONFIGURE ZONE

See #51643 for background.

ANALYZE/CREATE STATISTICS will not be considered a schema change and were added in a separate PR, #57076
The SPLIT/UNSPLIT features will also be resolved in a separate PR, as the execution path is different from the schema changes addressed in this PR.

---Commit message---

This change adds a feature flag via cluster setting for all
designated features that perform schema changes or DDLs. The
feature is being introduced to address a Cockroach Cloud SRE use
case: needing to disable certain categories of features, such as
schema changes, in case of cluster failure.

Release note (sql change): Adds a feature flag via cluster
setting for all schema change-related features. If a user attempts
to use these features while they are disabled, an error indicating
that the database administrator has disabled the feature is
surfaced.

Example usage for the database administrator:
SET CLUSTER SETTING feature.schemachange.enabled = FALSE;
SET CLUSTER SETTING feature.schemachange.enabled = TRUE;

[cockroach-teamcity]

This change is 

[otan]

this is awesome! two small changes requested.

Reviewed 41 of 41 files at r1.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @angelapwen and @pbardea)

---

pkg/sql/alter_database.go, line 36 at r1 (raw file):

	if err := featureflag.CheckEnabled(featureSchemaChangeEnabled,
		&p.ExecCfg().Settings.SV,
		"ALTER DATABASE is part of the schema change category, which",

if we're including this message for all schema changes, might be worth adding a helper function so you only put ALTER DATABASE here. maybe put the function in this package so the featureflag package is schema change agnostic.

---

pkg/sql/create_stats.go, line 55 at r1 (raw file):

	if err := featureflag.CheckEnabled(featureSchemaChangeEnabled,
		&p.ExecCfg().Settings.SV,
		"ANALYZE/CREATE STATS is part of the schema change category, which"); err != nil {

i think these aren't schema changes -- might be worth creating a separate PR and put this as part of the CREATE_STATS or ANALYZE flag.

---

pkg/sql/schema_change_cluster_setting.go, line 24 at r1 (raw file):

// package?
var featureSchemaChangeEnabled = settings.RegisterPublicBoolSetting(
	"feature.schemachange.enabled",

can we make this schema_change since it is two words?

[otan]

oops, premature accept.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @angelapwen and @pbardea)

[angelapwen]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @otan and @pbardea)

---

pkg/sql/alter_database.go, line 36 at r1 (raw file):

Previously, otan (Oliver Tan) wrote…

if we're including this message for all schema changes, might be worth adding a helper function so you only put ALTER DATABASE here. maybe put the function in this package so the featureflag package is schema change agnostic.

Yeah, that makes sense. I'll put it under the schema_change_cluster_setting package where I register the settings.

---

pkg/sql/create_stats.go, line 55 at r1 (raw file):

Previously, otan (Oliver Tan) wrote…

i think these aren't schema changes -- might be worth creating a separate PR and put this as part of the CREATE_STATS or ANALYZE flag.

Ah alright!

---

pkg/sql/schema_change_cluster_setting.go, line 24 at r1 (raw file):

Previously, otan (Oliver Tan) wrote…

can we make this schema_change since it is two words?

Yes!

[otan]

Looks like two small failures left.

go test ./pkg/sql/pgwire -run TestPGTest/notice -rewrite to fix the notice one!

Reviewed 42 of 42 files at r2.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @otan)

[angelapwen]

Thanks! I think I've addressed the two failures just now.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @otan)

[angelapwen]

bors r=otan

[otan]

lgtm

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @otan)

[craig]

Build failed:

• GitHub CI (Cockroach)

[angelapwen]

Flaky roachtest, giving this another go 🙏

bors r=otan

[craig]

Build succeeded:

• GitHub CI (Cockroach)