*: add warnings to slow log and slow query table

executor/adapter.go

@@ -1554,6 +1554,7 @@ func (a *ExecStmt) LogSlowQuery(txnTS uint64, succ bool, hasMoreResults bool) {
 		IsWriteCacheTable: stmtCtx.WaitLockLeaseTime > 0,
 		StatsLoadStatus:   convertStatusIntoString(a.Ctx, stmtCtx.StatsLoadStatus),
 		IsSyncStatsFailed: stmtCtx.IsSyncStatsFailed,
+		Warnings:          collectWarningsForSlowLog(stmtCtx),
 	}
 	failpoint.Inject("assertSyncStatsFailed", func(val failpoint.Value) {
 		if val.(bool) {
@@ -1609,6 +1610,33 @@ func (a *ExecStmt) LogSlowQuery(txnTS uint64, succ bool, hasMoreResults bool) {
 	}
 }
 
+func extractMsgFromSQLWarn(SQLWarn *stmtctx.SQLWarn) string {
+	// Currently, this function is only used in collectWarningsForSlowLog.
+	// collectWarningsForSlowLog can make sure SQLWarn is not nil so no need to add a nil check here.
+	warn := errors.Cause(SQLWarn.Err)
+	if x, ok := warn.(*terror.Error); ok && x != nil {
+		sqlErr := terror.ToSQLError(x)
+		return sqlErr.Message
+	}
+	return warn.Error()
+}
+
+func collectWarningsForSlowLog(stmtCtx *stmtctx.StatementContext) []variable.JSONSQLWarnForSlowLog {
+	warnings := stmtCtx.GetWarnings()
+	extraWarnings := stmtCtx.GetExtraWarnings()
+	res := make([]variable.JSONSQLWarnForSlowLog, len(warnings)+len(extraWarnings))
+	for i := range warnings {
+		res[i].Level = warnings[i].Level
+		res[i].Message = extractMsgFromSQLWarn(&warnings[i])
+	}
+	for i := range extraWarnings {
+		res[len(warnings)+i].Level = extraWarnings[i].Level
+		res[len(warnings)+i].Message = extractMsgFromSQLWarn(&extraWarnings[i])
+		res[len(warnings)+i].IsExtra = true
+	}
+	return res
+}
+
 // GetResultRowsCount gets the count of the statement result rows.
 func GetResultRowsCount(stmtCtx *stmtctx.StatementContext, p plannercore.Plan) int64 {
 	runtimeStatsColl := stmtCtx.RuntimeStatsColl

executor/main_test.go

@@ -33,17 +33,20 @@ var prepareMergeSuiteData testdata.TestData
 var aggMergeSuiteData testdata.TestData
 var executorSuiteData testdata.TestData
 var pointGetSuiteData testdata.TestData
+var slowQuerySuiteData testdata.TestData
 
 func TestMain(m *testing.M) {
 	testsetup.SetupForCommonTest()
 	testDataMap.LoadTestSuiteData("testdata", "agg_suite")
 	testDataMap.LoadTestSuiteData("testdata", "executor_suite")
 	testDataMap.LoadTestSuiteData("testdata", "prepare_suite")
 	testDataMap.LoadTestSuiteData("testdata", "point_get_suite")
+	testDataMap.LoadTestSuiteData("testdata", "slow_query_suite")
 	aggMergeSuiteData = testDataMap["agg_suite"]
 	executorSuiteData = testDataMap["executor_suite"]
 	prepareMergeSuiteData = testDataMap["prepare_suite"]
 	pointGetSuiteData = testDataMap["point_get_suite"]
+	slowQuerySuiteData = testDataMap["slow_query_suite"]
 
 	autoid.SetStep(5000)
 	config.UpdateGlobal(func(conf *config.Config) {

executor/slow_query.go

@@ -622,6 +622,9 @@ func (e *slowQueryRetriever) parseLog(ctx context.Context, sctx sessionctx.Conte
 					valid = e.setColumnValue(sctx, row, tz, variable.SlowLogHostStr, host, e.checker, fileLine)
 				} else if strings.HasPrefix(line, variable.SlowLogCopBackoffPrefix) {
 					valid = e.setColumnValue(sctx, row, tz, variable.SlowLogBackoffDetail, line, e.checker, fileLine)
+				} else if strings.HasPrefix(line, variable.SlowLogWarnings) {
+					line = line[len(variable.SlowLogWarnings+variable.SlowLogSpaceMarkStr):]
+					valid = e.setColumnValue(sctx, row, tz, variable.SlowLogWarnings, line, e.checker, fileLine)
 				} else {
 					fields, values := splitByColon(line)
 					for i := 0; i < len(fields); i++ {
@@ -781,7 +784,7 @@ func getColumnValueFactoryByName(sctx sessionctx.Context, colName string, column
 		}, nil
 	case variable.SlowLogUserStr, variable.SlowLogHostStr, execdetails.BackoffTypesStr, variable.SlowLogDBStr, variable.SlowLogIndexNamesStr, variable.SlowLogDigestStr,
 		variable.SlowLogStatsInfoStr, variable.SlowLogCopProcAddr, variable.SlowLogCopWaitAddr, variable.SlowLogPlanDigest,
-		variable.SlowLogPrevStmt, variable.SlowLogQuerySQLStr:
+		variable.SlowLogPrevStmt, variable.SlowLogQuerySQLStr, variable.SlowLogWarnings:
 		return func(row []types.Datum, value string, tz *time.Location, checker *slowLogChecker) (valid bool, err error) {
 			row[columnIdx] = types.NewStringDatum(value)
 			return true, nil

executor/slow_query_sql_test.go

@@ -23,6 +23,7 @@ import (
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/executor"
 	"github.com/pingcap/tidb/parser/auth"
+	"github.com/pingcap/tidb/parser/model"
 	"github.com/pingcap/tidb/testkit"
 	"github.com/pingcap/tidb/testkit/testdata"
 	"github.com/pingcap/tidb/util/logutil"
@@ -283,3 +284,61 @@ func TestIssue37066(t *testing.T) {
 		}
 	}
 }
+
+func TestWarningsInSlowQuery(t *testing.T) {
+	// Prepare the slow log
+	originCfg := config.GetGlobalConfig()
+	newCfg := *originCfg
+	f, err := os.CreateTemp("", "tidb-slow-*.log")
+	require.NoError(t, err)
+	newCfg.Log.SlowQueryFile = f.Name()
+	config.StoreGlobalConfig(&newCfg)
+	defer func() {
+		config.StoreGlobalConfig(originCfg)
+		require.NoError(t, f.Close())
+		require.NoError(t, os.Remove(newCfg.Log.SlowQueryFile))
+	}()
+	require.NoError(t, logutil.InitLogger(newCfg.Log.ToLogConfig()))
+	store, dom := testkit.CreateMockStoreAndDomain(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec(fmt.Sprintf("set @@tidb_slow_query_file='%v'", f.Name()))
+	tk.MustExec("set tidb_slow_log_threshold=0;")
+	defer func() {
+		tk.MustExec("set tidb_slow_log_threshold=300;")
+	}()
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int, b int, c int, d int, e int, f int, g int, h set('11', '22', '33')," +
+		"primary key (a), unique key c_d_e (c, d, e), unique key f (f), unique key f_g (f, g), key g (g))")
+	tbl, err := dom.InfoSchema().TableByName(model.CIStr{O: "test", L: "test"}, model.CIStr{O: "t", L: "t"})
+	require.NoError(t, err)
+	tbl.Meta().TiFlashReplica = &model.TiFlashReplicaInfo{Count: 1, Available: true}
+
+	var input []string
+	var output []struct {
+		SQL    string
+		Result string
+	}
+	slowQuerySuiteData.LoadTestCases(t, &input, &output)
+	for i, test := range input {
+		comment := fmt.Sprintf("case:%v sql:%s", i, test)
+		if len(test) < 6 || test[:6] != "select" {
+			tk.MustExec(test)
+		} else {
+			tk.MustQuery(test)
+		}
+		res := testdata.ConvertRowsToStrings(
+			tk.MustQuery("select warnings from information_schema.slow_query " +
+				`where query = "` + test + `;" ` +
+				"order by time desc limit 1").Rows(),
+		)
+		require.Lenf(t, res, 1, comment)
+
+		testdata.OnRecord(func() {
+			output[i].SQL = test
+			output[i].Result = res[0]
+		})
+		require.Equal(t, output[i].Result, res[0])
+	}
+}

executor/slow_query_test.go

@@ -160,7 +160,7 @@ select * from t;`
 	expectRecordString := `2019-04-28 15:24:04.309074,` +
 		`405888132465033227,root,localhost,0,57,0.12,0.216905,` +
 		`0,0,0,0,0,0,0,0,0,0,0,0,,0,0,0,0,0,0,0.38,0.021,0,0,0,1,637,0,10,10,10,10,100,,,1,42a1c8aae6f133e934d4bf0147491709a8812ea05ff8819ec522780fe657b772,t1:1,t2:2,` +
-		`0.1,0.2,0.03,127.0.0.1:20160,0.05,0.6,0.8,0.0.0.0:20160,70724,65536,0,0,0,0,0,` +
+		`0.1,0.2,0.03,127.0.0.1:20160,0.05,0.6,0.8,0.0.0.0:20160,70724,65536,0,0,0,0,0,,` +
 		`Cop_backoff_regionMiss_total_times: 200 Cop_backoff_regionMiss_total_time: 0.2 Cop_backoff_regionMiss_max_time: 0.2 Cop_backoff_regionMiss_max_addr: 127.0.0.1 Cop_backoff_regionMiss_avg_time: 0.2 Cop_backoff_regionMiss_p90_time: 0.2 Cop_backoff_rpcPD_total_times: 200 Cop_backoff_rpcPD_total_time: 0.2 Cop_backoff_rpcPD_max_time: 0.2 Cop_backoff_rpcPD_max_addr: 127.0.0.1 Cop_backoff_rpcPD_avg_time: 0.2 Cop_backoff_rpcPD_p90_time: 0.2 Cop_backoff_rpcTiKV_total_times: 200 Cop_backoff_rpcTiKV_total_time: 0.2 Cop_backoff_rpcTiKV_max_time: 0.2 Cop_backoff_rpcTiKV_max_addr: 127.0.0.1 Cop_backoff_rpcTiKV_avg_time: 0.2 Cop_backoff_rpcTiKV_p90_time: 0.2,` +
 		`0,0,1,0,1,1,0,,60e9378c746d9a2be1c791047e008967cf252eb6de9167ad3aa6098fa2d523f4,` +
 		`,update t set i = 1;,select * from t;`
@@ -183,7 +183,7 @@ select * from t;`
 	expectRecordString = `2019-04-28 15:24:04.309074,` +
 		`405888132465033227,root,localhost,0,57,0.12,0.216905,` +
 		`0,0,0,0,0,0,0,0,0,0,0,0,,0,0,0,0,0,0,0.38,0.021,0,0,0,1,637,0,10,10,10,10,100,,,1,42a1c8aae6f133e934d4bf0147491709a8812ea05ff8819ec522780fe657b772,t1:1,t2:2,` +
-		`0.1,0.2,0.03,127.0.0.1:20160,0.05,0.6,0.8,0.0.0.0:20160,70724,65536,0,0,0,0,0,` +
+		`0.1,0.2,0.03,127.0.0.1:20160,0.05,0.6,0.8,0.0.0.0:20160,70724,65536,0,0,0,0,0,,` +
 		`Cop_backoff_regionMiss_total_times: 200 Cop_backoff_regionMiss_total_time: 0.2 Cop_backoff_regionMiss_max_time: 0.2 Cop_backoff_regionMiss_max_addr: 127.0.0.1 Cop_backoff_regionMiss_avg_time: 0.2 Cop_backoff_regionMiss_p90_time: 0.2 Cop_backoff_rpcPD_total_times: 200 Cop_backoff_rpcPD_total_time: 0.2 Cop_backoff_rpcPD_max_time: 0.2 Cop_backoff_rpcPD_max_addr: 127.0.0.1 Cop_backoff_rpcPD_avg_time: 0.2 Cop_backoff_rpcPD_p90_time: 0.2 Cop_backoff_rpcTiKV_total_times: 200 Cop_backoff_rpcTiKV_total_time: 0.2 Cop_backoff_rpcTiKV_max_time: 0.2 Cop_backoff_rpcTiKV_max_addr: 127.0.0.1 Cop_backoff_rpcTiKV_avg_time: 0.2 Cop_backoff_rpcTiKV_p90_time: 0.2,` +
 		`0,0,1,0,1,1,0,,60e9378c746d9a2be1c791047e008967cf252eb6de9167ad3aa6098fa2d523f4,` +
 		`,update t set i = 1;,select * from t;`

executor/testdata/slow_query_suite_in.json

@@ -0,0 +1,19 @@
+[
+  {
+    "name": "TestWarningsInSlowQuery",
+    "cases": [
+      "insert into t(a) value (1)",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ a/0 from t",
+      "create binding for select * from t where c = 10 using select * from t use index (c_d_e) where c = 10",
+      "select * from t where c = 10",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where a > 1 order by f",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where f > 1",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ f from t where f > 1",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where f > 3 and g = 5",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where g = 5 order by f",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where d = 3 order by c, e",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where h = '11,22'",
+      "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where a > rand()*100"
+    ]
+  }
+]

executor/testdata/slow_query_suite_out.json

@@ -0,0 +1,55 @@
+[
+  {
+    "Name": "TestWarningsInSlowQuery",
+    "Cases": [
+      {
+        "SQL": "insert into t(a) value (1)",
+        "Result": ""
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ a/0 from t",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Division by 0\"}]"
+      },
+      {
+        "SQL": "create binding for select * from t where c = 10 using select * from t use index (c_d_e) where c = 10",
+        "Result": ""
+      },
+      {
+        "SQL": "select * from t where c = 10",
+        "Result": "[{\"Level\":\"Note\",\"Message\":\"Using the bindSQL: SELECT * FROM `test`.`t` USE INDEX (`c_d_e`) WHERE `c` = 10\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where a > 1 order by f",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash)] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true},{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash),f,f_g] remain after pruning paths for t given Prop{SortItems: [{test.t.f asc}], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where f > 1",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash),f,f_g] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ f from t where f > 1",
+        "Result": "[{\"Level\":\"Note\",\"Message\":\"[t(tiflash),f,f_g] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where f > 3 and g = 5",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash),f_g,g] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where g = 5 order by f",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash),g] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true},{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash),f_g,g] remain after pruning paths for t given Prop{SortItems: [{test.t.f asc}], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where d = 3 order by c, e",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash)] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true},{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash),c_d_e] remain after pruning paths for t given Prop{SortItems: [{test.t.c asc} {test.t.e asc}], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where h = '11,22'",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash)] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      },
+      {
+        "SQL": "select /*+ READ_FROM_STORAGE(TIKV[t]) */ * from t where a > rand()*100",
+        "Result": "[{\"Level\":\"Warning\",\"Message\":\"Scalar function 'rand'(signature: Rand, return type: double) is not supported to push down to storage layer now.\",\"IsExtra\":true},{\"Level\":\"Warning\",\"Message\":\"Expression about 'test.t.h' can not be pushed to TiFlash because it contains unsupported calculation of type 'set'.\",\"IsExtra\":true},{\"Level\":\"Warning\",\"Message\":\"Scalar function 'rand'(signature: Rand, return type: double) is not supported to push down to tiflash now.\",\"IsExtra\":true},{\"Level\":\"Note\",\"Message\":\"[t,t(tiflash)] remain after pruning paths for t given Prop{SortItems: [], TaskTp: rootTask}\",\"IsExtra\":true}]"
+      }
+    ]
+  }
+]

infoschema/tables.go

@@ -890,6 +890,7 @@ var slowQueryCols = []columnInfo{
 	{name: variable.SlowLogBackoffTotal, tp: mysql.TypeDouble, size: 22},
 	{name: variable.SlowLogWriteSQLRespTotal, tp: mysql.TypeDouble, size: 22},
 	{name: variable.SlowLogResultRows, tp: mysql.TypeLonglong, size: 22},
+	{name: variable.SlowLogWarnings, tp: mysql.TypeLongBlob, size: types.UnspecifiedLength},
 	{name: variable.SlowLogBackoffDetail, tp: mysql.TypeVarchar, size: 4096},
 	{name: variable.SlowLogPrepared, tp: mysql.TypeTiny, size: 1},
 	{name: variable.SlowLogSucc, tp: mysql.TypeTiny, size: 1},

infoschema/tables_test.go

@@ -597,6 +597,7 @@ func TestSlowQuery(t *testing.T) {
 			"0",
 			"10",
 			"",
+			"",
 			"0",
 			"1",
 			"0",
@@ -670,6 +671,7 @@ func TestSlowQuery(t *testing.T) {
 			"0",
 			"0",
 			"",
+			"",
 			"0",
 			"1",
 			"0",

sessionctx/variable/session.go

@@ -19,6 +19,7 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/binary"
+	"encoding/json"
 	"fmt"
 	"math"
 	"math/rand"
@@ -2735,6 +2736,9 @@ const (
 	SlowLogBackoffDetail = "Backoff_Detail"
 	// SlowLogResultRows is the row count of the SQL result.
 	SlowLogResultRows = "Result_rows"
+	// SlowLogWarnings is the warnings generated during executing the statement.
+	// Note that some extra warnings would also be printed through slow log.
+	SlowLogWarnings = "Warnings"
 	// SlowLogIsExplicitTxn is used to indicate whether this sql execute in explicit transaction or not.
 	SlowLogIsExplicitTxn = "IsExplicitTxn"
 	// SlowLogIsWriteCacheTable is used to indicate whether writing to the cache table need to wait for the read lock to expire.
@@ -2747,6 +2751,15 @@ const (
 // It's controlled by the global variable `tidb_generate_binary_plan`.
 var GenerateBinaryPlan atomic2.Bool
 
+// JSONSQLWarnForSlowLog helps to print the SQLWarn through the slow log in JSON format.
+type JSONSQLWarnForSlowLog struct {
+	Level   string
+	Message string
+	// IsExtra means this SQL Warn is expected to be recorded only under some conditions (like in EXPLAIN) and should
+	// haven't been recorded as a warning now, but we recorded it anyway to help diagnostics.
+	IsExtra bool `json:",omitempty"`
+}
+
 // SlowQueryLogItems is a collection of items that should be included in the
 // slow query log.
 type SlowQueryLogItems struct {
@@ -2786,6 +2799,7 @@ type SlowQueryLogItems struct {
 	// table -> name -> status
 	StatsLoadStatus   map[string]map[string]string
 	IsSyncStatsFailed bool
+	Warnings          []JSONSQLWarnForSlowLog
 }
 
 // SlowLogFormat uses for formatting slow log.
@@ -2951,6 +2965,16 @@ func (s *SessionVars) SlowLogFormat(logItems *SlowQueryLogItems) string {
 	writeSlowLogItem(&buf, SlowLogBackoffTotal, strconv.FormatFloat(logItems.BackoffTotal.Seconds(), 'f', -1, 64))
 	writeSlowLogItem(&buf, SlowLogWriteSQLRespTotal, strconv.FormatFloat(logItems.WriteSQLRespTotal.Seconds(), 'f', -1, 64))
 	writeSlowLogItem(&buf, SlowLogResultRows, strconv.FormatInt(logItems.ResultRows, 10))
+	if len(logItems.Warnings) > 0 {
+		buf.WriteString(SlowLogRowPrefixStr + SlowLogWarnings + SlowLogSpaceMarkStr)
+		jsonEncoder := json.NewEncoder(&buf)
+		jsonEncoder.SetEscapeHTML(false)
+		// Note that the Encode() will append a '\n' so we don't need to add another.
+		err := jsonEncoder.Encode(logItems.Warnings)
+		if err != nil {
+			buf.WriteString(err.Error())
+		}
+	}
 	writeSlowLogItem(&buf, SlowLogSucc, strconv.FormatBool(logItems.Succ))
 	writeSlowLogItem(&buf, SlowLogIsExplicitTxn, strconv.FormatBool(logItems.IsExplicitTxn))
 	writeSlowLogItem(&buf, SlowLogIsSyncStatsFailed, strconv.FormatBool(logItems.IsSyncStatsFailed))