pgwire: add telemetry for fetch limits

The JDBC driver and perhaps others commonly try to use the "fetch
limit" parameter, which is yet unsupported in
CockroachDB (cockroachdb#4035). This patch adds telemetry to gauge demand.

Release note (sql change): attempts by client apps to use the
unsupported "fetch limit" parameter (e.g. via JDBC) will now be
captured in telemetry if statistics reporting is enabled, to gauge
support for this feature.

pkg/server/telemetry/features.go

@@ -18,6 +18,8 @@ import (
 	"fmt"
 	"sync/atomic"
 
+	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
+	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/syncutil"
 )
 
@@ -123,3 +125,36 @@ func GetAndResetFeatureCounts(quantize bool) map[string]int32 {
 	}
 	return m
 }
+
+// RecordError takes an error and increments the corresponding count
+// for its error code, and, if it is an unimplemented or internal
+// error, the count for that feature or the internal error's shortened
+// stack trace.
+func RecordError(err error) {
+	if err == nil {
+		return
+	}
+
+	if pgErr, ok := pgerror.GetPGCause(err); ok {
+		Count("errorcodes." + pgErr.Code)
+
+		if details := pgErr.InternalCommand; details != "" {
+			var prefix string
+			switch pgErr.Code {
+			case pgerror.CodeFeatureNotSupportedError:
+				prefix = "unimplemented."
+			case pgerror.CodeInternalError:
+				prefix = "internalerror."
+			default:
+				prefix = "othererror." + pgErr.Code + "."
+			}
+			Count(prefix + details)
+		}
+	} else {
+		typ := log.ErrorSource(err)
+		if typ == "" {
+			typ = "unknown"
+		}
+		Count("othererror." + typ)
+	}
+}

pkg/sql/conn_executor.go

@@ -303,39 +303,6 @@ func (s *Server) Start(ctx context.Context, stopper *stop.Stopper) {
 	s.PeriodicallyClearStmtStats(ctx, stopper)
 }
 
-// recordError takes an error and increments the corresponding count
-// for its error code, and, if it is an unimplemented or internal
-// error, the count for that feature or the internal error's shortened
-// stack trace.
-func (s *Server) recordError(err error) {
-	if err == nil {
-		return
-	}
-
-	if pgErr, ok := pgerror.GetPGCause(err); ok {
-		telemetry.Count("errorcodes." + pgErr.Code)
-
-		if details := pgErr.InternalCommand; details != "" {
-			var prefix string
-			switch pgErr.Code {
-			case pgerror.CodeFeatureNotSupportedError:
-				prefix = "unimplemented."
-			case pgerror.CodeInternalError:
-				prefix = "internalerror."
-			default:
-				prefix = "othererror." + pgErr.Code + "."
-			}
-			telemetry.Count(prefix + details)
-		}
-	} else {
-		typ := log.ErrorSource(err)
-		if typ == "" {
-			typ = "unknown"
-		}
-		telemetry.Count("othererror." + typ)
-	}
-}
-
 // ResetStatementStats resets the executor's collected statement statistics.
 func (s *Server) ResetStatementStats(ctx context.Context) {
 	s.sqlStats.resetStats(ctx)
@@ -1293,12 +1260,12 @@ func (ex *connExecutor) run(
 				ex.sessionEventf(ex.Ctx(), "execution error: %s", pe.errorCause())
 			}
 			if resErr == nil && ok {
-				ex.server.recordError(pe.errorCause())
+				telemetry.RecordError(pe.errorCause())
 				// Depending on whether the result has the error already or not, we have
 				// to call either Close or CloseWithErr.
 				res.CloseWithErr(pe.errorCause())
 			} else {
-				ex.server.recordError(resErr)
+				telemetry.RecordError(resErr)
 				res.Close(stateToTxnStatusIndicator(ex.machine.CurState()))
 			}
 		} else {

pkg/sql/conn_executor_exec.go

@@ -26,6 +26,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/base"
 	"github.com/cockroachdb/cockroach/pkg/internal/client"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
+	"github.com/cockroachdb/cockroach/pkg/server/telemetry"
 	"github.com/cockroachdb/cockroach/pkg/sql/coltypes"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
@@ -1207,7 +1208,7 @@ func (ex *connExecutor) runShowSyntax(
 			commErr = res.AddRow(ctx, tree.Datums{tree.NewDString(field), tree.NewDString(msg)})
 			return nil
 		},
-		ex.server.recordError, /* reportErr */
+		telemetry.RecordError, /* reportErr */
 	); err != nil {
 		res.SetError(err)
 	}

pkg/sql/pgwire/command_result.go

@@ -18,13 +18,14 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/cockroachdb/cockroach/pkg/server/telemetry"
 	"github.com/cockroachdb/cockroach/pkg/sql"
+	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgwirebase"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
 	"github.com/cockroachdb/cockroach/pkg/sql/sessiondata"
 	"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
 	"github.com/lib/pq/oid"
-	"github.com/pkg/errors"
 )
 
 type completionMsgType int
@@ -124,9 +125,11 @@ func (r *commandResult) Close(t sql.TransactionStatusIndicator) {
 		r.typ == commandComplete &&
 		r.stmtType == tree.Rows {
 
-		r.err = errors.Errorf("execute row count limits not supported: %d of %d",
+		r.err = pgerror.UnimplementedWithIssueErrorf(4035,
+			"execute row count limits not supported: %d of %d",
 			r.limit, r.rowsAffected)
-		r.conn.bufferErr(convertToErrWithPGCode(r.err))
+		telemetry.RecordError(r.err)
+		r.conn.bufferErr(r.err)
 	}
 
 	// Send a completion message, specific to the type of result.