sql: simplifiy tracking of injected txn retry errors

Rather than using the txn epoch, we can just track how many errors were
injected. This lets us have a bit more control over how many errors to
inject, without having to rely on how the KV layer handles different
types of transaction retries.

Release note: None

pkg/sql/conn_executor_exec.go

@@ -1305,12 +1305,11 @@ func (ex *connExecutor) commitSQLTransaction(
 	ex.extraTxnState.idleLatency += ex.statsCollector.PhaseTimes().
 		GetIdleLatency(ex.statsCollector.PreviousPhaseTimes())
 	if ex.sessionData().InjectRetryErrorsOnCommitEnabled && ast.StatementTag() == "COMMIT" {
-		if ex.planner.Txn().Epoch() < ex.state.lastEpoch+numTxnRetryErrors {
+		if ex.state.injectedTxnRetryCounter < numTxnRetryErrors {
 			retryErr := ex.state.mu.txn.GenerateForcedRetryableErr(
 				ctx, "injected by `inject_retry_errors_on_commit_enabled` session variable")
+			ex.state.injectedTxnRetryCounter++
 			return ex.makeErrEvent(retryErr, ast)
-		} else {
-			ex.state.lastEpoch = ex.planner.Txn().Epoch()
 		}
 	}
 	ex.phaseTimes.SetSessionPhaseTime(sessionphase.SessionStartTransactionCommit, timeutil.Now())
@@ -1740,12 +1739,11 @@ func (ex *connExecutor) dispatchToExecutionEngine(
 		isSetOrShow := stmt.AST.StatementTag() == "SET" || stmt.AST.StatementTag() == "SHOW"
 		if ex.sessionData().InjectRetryErrorsEnabled && !isSetOrShow &&
 			planner.Txn().Sender().TxnStatus() == roachpb.PENDING {
-			if planner.Txn().Epoch() < ex.state.lastEpoch+numTxnRetryErrors {
+			if ex.state.injectedTxnRetryCounter < numTxnRetryErrors {
 				retryErr := planner.Txn().GenerateForcedRetryableErr(
 					ctx, "injected by `inject_retry_errors_enabled` session variable")
 				res.SetError(retryErr)
-			} else {
-				ex.state.lastEpoch = planner.Txn().Epoch()
+				ex.state.injectedTxnRetryCounter++
 			}
 		}
 	}

pkg/sql/txn_state.go

@@ -22,7 +22,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
 	"github.com/cockroachdb/cockroach/pkg/sql/sessiondatapb"
-	"github.com/cockroachdb/cockroach/pkg/storage/enginepb"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 	"github.com/cockroachdb/cockroach/pkg/util/metric"
 	"github.com/cockroachdb/cockroach/pkg/util/mon"
@@ -108,8 +107,10 @@ type txnState struct {
 	// through the use of AS OF SYSTEM TIME.
 	isHistorical bool
 
-	// lastEpoch is the last observed epoch in the current txn.
-	lastEpoch enginepb.TxnEpoch
+	// injectedTxnRetryCounter keeps track of how many errors have been
+	// injected in this transaction with the inject_retry_errors_enabled
+	// flag.
+	injectedTxnRetryCounter int
 
 	// mon tracks txn-bound objects like the running state of
 	// planNode in the midst of performing a computation.
@@ -191,7 +192,7 @@ func (ts *txnState) resetForNewSQLTxn(
 	// Reset state vars to defaults.
 	ts.sqlTimestamp = sqlTimestamp
 	ts.isHistorical = false
-	ts.lastEpoch = 0
+	ts.injectedTxnRetryCounter = 0
 
 	// Create a context for this transaction. It will include a root span that
 	// will contain everything executed as part of the upcoming SQL txn, including