sql: new cluster setting for index recommendation

As part of cockroachdb#83782, we will generate index recommendation
per statement fingerprint id. As a safety, creating the
cluster setting
`sql.metrics.statement_details.index_recommendation_collection.enabled`
that can be disable, in case there are any issues with
performance.

Release note (sql change): Creation of cluster setting
`sql.metrics.statement_details.index_recommendation_collection.enabled`
that can be disabled if index recommendation generation is
causing performance issues.

docs/generated/settings/settings-for-tenants.txt

@@ -239,6 +239,7 @@ sql.metrics.max_mem_stmt_fingerprints	integer	100000	the maximum number of state
 sql.metrics.max_mem_txn_fingerprints	integer	100000	the maximum number of transaction fingerprints stored in memory
 sql.metrics.statement_details.dump_to_logs	boolean	false	dump collected statement statistics to node logs when periodically cleared
 sql.metrics.statement_details.enabled	boolean	true	collect per-statement query statistics
+sql.metrics.statement_details.index_recommendation_collection.enabled	boolean	true	generate an index recommendation for each fingerprint ID
 sql.metrics.statement_details.plan_collection.enabled	boolean	true	periodically save a logical plan for each fingerprint
 sql.metrics.statement_details.plan_collection.period	duration	5m0s	the time until a new logical plan is collected
 sql.metrics.statement_details.threshold	duration	0s	minimum execution time to cause statement statistics to be collected. If configured, no transaction stats are collected.

docs/generated/settings/settings.html

@@ -170,6 +170,7 @@
 <tr><td><code>sql.metrics.max_mem_txn_fingerprints</code></td><td>integer</td><td><code>100000</code></td><td>the maximum number of transaction fingerprints stored in memory</td></tr>
 <tr><td><code>sql.metrics.statement_details.dump_to_logs</code></td><td>boolean</td><td><code>false</code></td><td>dump collected statement statistics to node logs when periodically cleared</td></tr>
 <tr><td><code>sql.metrics.statement_details.enabled</code></td><td>boolean</td><td><code>true</code></td><td>collect per-statement query statistics</td></tr>
+<tr><td><code>sql.metrics.statement_details.index_recommendation_collection.enabled</code></td><td>boolean</td><td><code>true</code></td><td>generate an index recommendation for each fingerprint ID</td></tr>
 <tr><td><code>sql.metrics.statement_details.plan_collection.enabled</code></td><td>boolean</td><td><code>true</code></td><td>periodically save a logical plan for each fingerprint</td></tr>
 <tr><td><code>sql.metrics.statement_details.plan_collection.period</code></td><td>duration</td><td><code>5m0s</code></td><td>the time until a new logical plan is collected</td></tr>
 <tr><td><code>sql.metrics.statement_details.threshold</code></td><td>duration</td><td><code>0s</code></td><td>minimum execution time to cause statement statistics to be collected. If configured, no transaction stats are collected.</td></tr>

pkg/sql/sqlstats/cluster_settings.go

@@ -159,3 +159,12 @@ var MaxSQLStatReset = settings.RegisterDurationSetting(
 	time.Hour*2,
 	settings.NonNegativeDurationWithMaximum(time.Hour*24),
 ).WithPublic()
+
+// SampleIndexRecommendation specifies whether we generate an index recommendation
+// for each fingerprint ID.
+var SampleIndexRecommendation = settings.RegisterBoolSetting(
+	settings.TenantWritable,
+	"sql.metrics.statement_details.index_recommendation_collection.enabled",
+	"generate an index recommendation for each fingerprint ID",
+	true,
+).WithPublic()