sql/telemetry: add SkippedTransactions to SampledTransaction proto

This commit adds the field SkippedTransactions to the
SampledTransaction protobuf to count the number of transactions
that were not sampled while telemetry transaction logging
is enabled. The corresponding field is added to the
telemetryLogging struct and will be used in the following
commit to track skipped transactions. Some whitespace in the
SampledTransaction proto definition is adjusted.

Epic: none

Release note (sql change): New field `SkippedTransactions` in
the SampledTransaction event, which is emitted to the TELEMETRY
logging channel when telemetry logging is enabled and set to
"transaction" mode.

docs/generated/eventlog.md

@@ -3081,6 +3081,7 @@ An event of type `sampled_transaction` is the event logged to telemetry at the e
 | `RowsRead` | RowsRead is the number of rows read from disk. | no |
 | `RowsWritten` | RowsWritten is the number of rows written to disk. | no |
 | `SampledExecStats` | SampledExecStats is a nested field containing execution statistics. This field will be omitted if the stats were not sampled. | yes |
+| `SkippedTransactions` | SkippedTransactions is the number of transactions that were skipped as part of sampling prior to this one. We only count skipped transactions when telemetry logging is enabled and the sampling mode is set to "transaction". | no |
 
 
 #### Common fields

pkg/sql/telemetry_logging.go

@@ -125,6 +125,9 @@ type telemetryLoggingMetrics struct {
 
 	// skippedQueryCount is used to produce the count of non-sampled queries.
 	skippedQueryCount atomic.Uint64
+
+	// skippedTransactionCount is used to produce the count of non-sampled transactions.
+	skippedTransactionCount atomic.Uint64
 }
 
 func newTelemetryLoggingMetrics(
@@ -333,3 +336,11 @@ func (t *telemetryLoggingMetrics) resetLastSampledTime() {
 	defer t.mu.Unlock()
 	t.mu.lastSampledTime = time.Time{}
 }
+
+func (t *TelemetryLoggingMetrics) resetSkippedTransactionCount() (res uint64) {
+	return t.skippedTransactionCount.Swap(0)
+}
+
+func (t *TelemetryLoggingMetrics) incSkippedTransactionCount() {
+	t.skippedTransactionCount.Add(1)
+}

pkg/util/log/eventpb/telemetry.proto

@@ -457,27 +457,32 @@ message SampledTransaction {
   int64 num_rows = 18 [(gogoproto.jsontag) = ",includeempty"];
 
   // RetryLatNanos is the amount of time spent retrying the transaction.
- int64 retry_lat_nanos  = 19 [(gogoproto.jsontag) = ",omitempty"];
+  int64 retry_lat_nanos  = 19 [(gogoproto.jsontag) = ",omitempty"];
 
- // CommitLatNanos is the amount of time spent committing the transaction after all statement operations.
- int64 commit_lat_nanos = 20 [(gogoproto.jsontag) = ",includeempty"];
+  // CommitLatNanos is the amount of time spent committing the transaction after all statement operations.
+  int64 commit_lat_nanos = 20 [(gogoproto.jsontag) = ",includeempty"];
 
- // IdleLatNanos is the amount of time spent waiting for the client to send statements
+  // IdleLatNanos is the amount of time spent waiting for the client to send statements
   // while the transaction is open.
- int64 idle_lat_nanos = 21 [(gogoproto.jsontag) = ",includeempty"];
+  int64 idle_lat_nanos = 21 [(gogoproto.jsontag) = ",includeempty"];
 
- // BytesRead is the number of bytes read from disk.
- int64 bytes_read = 22 [(gogoproto.jsontag) = ",includeempty"];
+  // BytesRead is the number of bytes read from disk.
+  int64 bytes_read = 22 [(gogoproto.jsontag) = ",includeempty"];
 
- // RowsRead is the number of rows read from disk.
- int64 rows_read = 23 [(gogoproto.jsontag) = ",includeempty"];
+  // RowsRead is the number of rows read from disk.
+  int64 rows_read = 23 [(gogoproto.jsontag) = ",includeempty"];
 
- // RowsWritten is the number of rows written to disk.
- int64 rows_written = 24 [(gogoproto.jsontag) = ",includeempty"];
+  // RowsWritten is the number of rows written to disk.
+  int64 rows_written = 24 [(gogoproto.jsontag) = ",includeempty"];
 
- // SampledExecStats is a nested field containing execution statistics.
- // This field will be omitted if the stats were not sampled.
- SampledExecStats sampled_exec_stats = 25 [(gogoproto.jsontag) = ",omitempty"];
+  // SampledExecStats is a nested field containing execution statistics.
+  // This field will be omitted if the stats were not sampled.
+  SampledExecStats sampled_exec_stats = 25 [(gogoproto.jsontag) = ",omitempty"];
+
+  // SkippedTransactions is the number of transactions that were skipped as part of sampling prior to
+  // this one. We only count skipped transactions when telemetry logging is enabled and the sampling
+  // mode is set to "transaction".
+  int64 skipped_transactions = 26 [(gogoproto.jsontag) = ",omitempty"];
 }
 
 // CapturedIndexUsageStats