Merge cockroachdb#34231

34231: sql: use time-based sampling for logical plans r=knz a=celiala

Previously, the rate at which we sampled logical plans was once every 1000th
time that fingerprint was executed. This diff changes the sampling rate from
count-based (once every 1000th execution) to a time-based cluster setting
(the default is set to once every 5 minutes).

This solves the following:
- For fingerprints with high execution counts, this prevent us from sampling
  too often and creating unnecessary overhead.
- For fingerprints with lower execution counts, this allows us to refresh
  plans more frequently, which could be helpful if a user wants to verify
  that a configuration change has improved a fingerprint's logical plan and
  execution time.
- Because stats are stored per node, having a timestamp additionally means
  that the UI can now determine and surface the plan that's the most
  recent across all nodes.
- This also solves an edge case where statementStatistics might exist
  without a sample, which can happen if user has set
  `sql.metrics.statement_details.plan_collection.enabled` to false, or if the
  stats were collected before this feature was introduced.

Release note: None

Co-authored-by: Celia La <celia@cockroachlabs.com>

docs/generated/settings/settings.html

@@ -78,7 +78,8 @@
 <tr><td><code>sql.distsql.temp_storage.workmem</code></td><td>byte size</td><td><code>64 MiB</code></td><td>maximum amount of memory in bytes a processor can use before falling back to temp storage</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.sample_logical_plans</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.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 statistics to be collected</td></tr>
 <tr><td><code>sql.parallel_scans.enabled</code></td><td>boolean</td><td><code>true</code></td><td>parallelizes scanning different ranges when the maximum result size can be deduced</td></tr>
 <tr><td><code>sql.query_cache.enabled</code></td><td>boolean</td><td><code>false</code></td><td>enable the query cache</td></tr>

pkg/roachpb/app_stats.proto

@@ -17,6 +17,7 @@ package cockroach.sql;
 option go_package = "roachpb";
 
 import "gogoproto/gogo.proto";
+import "google/protobuf/timestamp.proto";
 
 message StatementStatistics {
   // Count is the total number of times this statement was executed
@@ -88,6 +89,9 @@ message SensitiveInfo {
 
   // MostRecentPlanDescription is a serialized representation of the logical plan most recently captured for this query.
   optional ExplainTreePlanNode most_recent_plan_description = 2 [(gogoproto.nullable) = false];
+
+  // Timestamp is the time at which the logical plan was last sampled.
+  optional google.protobuf.Timestamp most_recent_plan_timestamp = 3 [(gogoproto.nullable) = false, (gogoproto.stdtime) = true];
 }
 
 message NumericStat {