Use system cursors for measurement, series, and tag key meta queries.

CHANGELOG.md

@@ -21,6 +21,7 @@
 - [#8662](https://github.com/influxdata/influxdb/pull/8662): Improve test coverage across both indexes.
 - [#8611](https://github.com/influxdata/influxdb/issues/8611): Respect X-Request-Id/Request-Id headers.
 - [#8572](https://github.com/influxdata/influxdb/issues/8668): InfluxDB now uses MIT licensed version of BurntSushi/toml.
+- [#8752](https://github.com/influxdata/influxdb/pull/8752): Use system cursors for measurement, series, and tag key meta queries.
 
 ### Bugfixes
 

coordinator/statement_executor.go

@@ -449,6 +449,7 @@ func (e *StatementExecutor) executeSelectStatement(stmt *influxql.SelectStatemen
 		em.Location = stmt.Location
 	}
 	em.OmitTime = stmt.OmitTime
+	em.EmitName = stmt.EmitName
 	defer em.Close()
 
 	// Emit rows to the results channel.

influxql/ast.go

@@ -1004,6 +1004,12 @@ type SelectStatement struct {
 	// Removes the "time" column from the output.
 	OmitTime bool
 
+	// Removes measurement name from resulting query. Useful for meta queries.
+	StripName bool
+
+	// Overrides the output measurement name.
+	EmitName string
+
 	// Removes duplicate rows from raw queries.
 	Dedupe bool
 }

influxql/statement_rewriter.go

@@ -88,21 +88,25 @@ func rewriteShowFieldKeyCardinalityStatement(stmt *ShowFieldKeyCardinalityStatem
 }
 
 func rewriteShowMeasurementsStatement(stmt *ShowMeasurementsStatement) (Statement, error) {
-	// Check for time in WHERE clause (not supported).
-	if HasTimeExpr(stmt.Condition) {
-		return nil, errors.New("SHOW MEASUREMENTS doesn't support time in WHERE clause")
-	}
-
-	condition := stmt.Condition
+	var sources Sources
 	if stmt.Source != nil {
-		condition = rewriteSourcesCondition(Sources([]Source{stmt.Source}), stmt.Condition)
+		sources = Sources{stmt.Source}
 	}
-	return &ShowMeasurementsStatement{
-		Database:   stmt.Database,
-		Condition:  condition,
-		Limit:      stmt.Limit,
+
+	return &SelectStatement{
+		Fields: []*Field{
+			{Expr: &VarRef{Val: "_name"}, Alias: "name"},
+		},
+		Sources:    rewriteSources2(sources, stmt.Database),
+		Condition:  stmt.Condition,
 		Offset:     stmt.Offset,
+		Limit:      stmt.Limit,
 		SortFields: stmt.SortFields,
+		OmitTime:   true,
+		StripName:  true,
+		EmitName:   "measurements",
+		Dedupe:     true,
+		IsRawQuery: true,
 	}, nil
 }
 
@@ -140,25 +144,22 @@ func rewriteShowMeasurementCardinalityStatement(stmt *ShowMeasurementCardinality
 		Offset:     stmt.Offset,
 		Limit:      stmt.Limit,
 		OmitTime:   true,
+		StripName:  true,
 	}, nil
 }
 
 func rewriteShowSeriesStatement(stmt *ShowSeriesStatement) (Statement, error) {
-	// Check for time in WHERE clause (not supported).
-	if HasTimeExpr(stmt.Condition) {
-		return nil, errors.New("SHOW SERIES doesn't support time in WHERE clause")
-	}
-
 	return &SelectStatement{
 		Fields: []*Field{
-			{Expr: &VarRef{Val: "key"}},
+			{Expr: &VarRef{Val: "_seriesKey"}, Alias: "key"},
 		},
-		Sources:    rewriteSources(stmt.Sources, "_series", stmt.Database),
-		Condition:  rewriteSourcesCondition(stmt.Sources, stmt.Condition),
+		Sources:    rewriteSources2(stmt.Sources, stmt.Database),
+		Condition:  stmt.Condition,
 		Offset:     stmt.Offset,
 		Limit:      stmt.Limit,
 		SortFields: stmt.SortFields,
 		OmitTime:   true,
+		StripName:  true,
 		Dedupe:     true,
 		IsRawQuery: true,
 	}, nil
@@ -248,11 +249,6 @@ func rewriteShowTagValuesStatement(stmt *ShowTagValuesStatement) (Statement, err
 }
 
 func rewriteShowTagValuesCardinalityStatement(stmt *ShowTagValuesCardinalityStatement) (Statement, error) {
-	// Check for time in WHERE clause (not supported).
-	if HasTimeExpr(stmt.Condition) {
-		return nil, errors.New("SHOW TAG VALUES CARDINALITY doesn't support time in WHERE clause")
-	}
-
 	// Use all measurements, if zero.
 	if len(stmt.Sources) == 0 {
 		stmt.Sources = Sources{
@@ -324,17 +320,18 @@ func rewriteShowTagValuesCardinalityStatement(stmt *ShowTagValuesCardinalityStat
 }
 
 func rewriteShowTagKeysStatement(stmt *ShowTagKeysStatement) (Statement, error) {
-	// Check for time in WHERE clause (not supported).
-	if HasTimeExpr(stmt.Condition) {
-		return nil, errors.New("SHOW TAG KEYS doesn't support time in WHERE clause")
-	}
-
 	return &SelectStatement{
 		Fields: []*Field{
-			{Expr: &VarRef{Val: "tagKey"}},
+			{
+				Expr: &Call{
+					Name: "distinct",
+					Args: []Expr{&VarRef{Val: "_tagKey"}},
+				},
+				Alias: "tagKey",
+			},
 		},
-		Sources:    rewriteSources(stmt.Sources, "_tagKeys", stmt.Database),
-		Condition:  rewriteSourcesCondition(stmt.Sources, stmt.Condition),
+		Sources:    rewriteSources2(stmt.Sources, stmt.Database),
+		Condition:  stmt.Condition,
 		Offset:     stmt.Offset,
 		Limit:      stmt.Limit,
 		SortFields: stmt.SortFields,
@@ -457,3 +454,20 @@ func rewriteSourcesCondition(sources Sources, cond Expr) Expr {
 	}
 	return scond
 }
+
+func rewriteSources2(sources Sources, database string) Sources {
+	if len(sources) == 0 {
+		sources = Sources{&Measurement{Regex: &RegexLiteral{Val: matchAllRegex.Copy()}}}
+	}
+	for _, source := range sources {
+		switch source := source.(type) {
+		case *Measurement:
+			if source.Database == "" {
+				source.Database = database
+			}
+		}
+	}
+	return sources
+}
+
+var matchAllRegex = regexp.MustCompile(`.+`)

influxql/statement_rewriter_test.go

@@ -53,91 +53,91 @@ func TestRewriteStatement(t *testing.T) {
 		},
 		{
 			stmt: `SHOW SERIES`,
-			s:    `SELECT "key" FROM _series`,
+			s:    `SELECT _seriesKey AS "key" FROM /.+/`,
 		},
 		{
 			stmt: `SHOW SERIES ON db0`,
-			s:    `SELECT "key" FROM db0.._series`,
+			s:    `SELECT _seriesKey AS "key" FROM db0../.+/`,
 		},
 		{
 			stmt: `SHOW SERIES FROM cpu`,
-			s:    `SELECT "key" FROM _series WHERE _name = 'cpu'`,
+			s:    `SELECT _seriesKey AS "key" FROM cpu`,
 		},
 		{
 			stmt: `SHOW SERIES ON db0 FROM cpu`,
-			s:    `SELECT "key" FROM db0.._series WHERE _name = 'cpu'`,
+			s:    `SELECT _seriesKey AS "key" FROM db0..cpu`,
 		},
 		{
 			stmt: `SHOW SERIES FROM mydb.myrp1.cpu`,
-			s:    `SELECT "key" FROM mydb.myrp1._series WHERE _name = 'cpu'`,
+			s:    `SELECT _seriesKey AS "key" FROM mydb.myrp1.cpu`,
 		},
 		{
 			stmt: `SHOW SERIES ON db0 FROM mydb.myrp1.cpu`,
-			s:    `SELECT "key" FROM mydb.myrp1._series WHERE _name = 'cpu'`,
+			s:    `SELECT _seriesKey AS "key" FROM mydb.myrp1.cpu`,
 		},
 		{
 			stmt: `SHOW SERIES FROM mydb.myrp1./c.*/`,
-			s:    `SELECT "key" FROM mydb.myrp1._series WHERE _name =~ /c.*/`,
+			s:    `SELECT _seriesKey AS "key" FROM mydb.myrp1./c.*/`,
 		},
 		{
 			stmt: `SHOW SERIES ON db0 FROM mydb.myrp1./c.*/`,
-			s:    `SELECT "key" FROM mydb.myrp1._series WHERE _name =~ /c.*/`,
+			s:    `SELECT _seriesKey AS "key" FROM mydb.myrp1./c.*/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS`,
-			s:    `SELECT tagKey FROM _tagKeys`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM /.+/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0`,
-			s:    `SELECT tagKey FROM db0.._tagKeys`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM db0../.+/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS FROM cpu`,
-			s:    `SELECT tagKey FROM _tagKeys WHERE _name = 'cpu'`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM cpu`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0 FROM cpu`,
-			s:    `SELECT tagKey FROM db0.._tagKeys WHERE _name = 'cpu'`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM db0..cpu`,
 		},
 		{
 			stmt: `SHOW TAG KEYS FROM /c.*/`,
-			s:    `SELECT tagKey FROM _tagKeys WHERE _name =~ /c.*/`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM /c.*/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0 FROM /c.*/`,
-			s:    `SELECT tagKey FROM db0.._tagKeys WHERE _name =~ /c.*/`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM db0../c.*/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS FROM cpu WHERE region = 'uswest'`,
-			s:    `SELECT tagKey FROM _tagKeys WHERE (_name = 'cpu') AND (region = 'uswest')`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM cpu WHERE region = 'uswest'`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0 FROM cpu WHERE region = 'uswest'`,
-			s:    `SELECT tagKey FROM db0.._tagKeys WHERE (_name = 'cpu') AND (region = 'uswest')`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM db0..cpu WHERE region = 'uswest'`,
 		},
 		{
 			stmt: `SHOW TAG KEYS FROM mydb.myrp1.cpu`,
-			s:    `SELECT tagKey FROM mydb.myrp1._tagKeys WHERE _name = 'cpu'`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM mydb.myrp1.cpu`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0 FROM mydb.myrp1.cpu`,
-			s:    `SELECT tagKey FROM mydb.myrp1._tagKeys WHERE _name = 'cpu'`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM mydb.myrp1.cpu`,
 		},
 		{
 			stmt: `SHOW TAG KEYS FROM mydb.myrp1./c.*/`,
-			s:    `SELECT tagKey FROM mydb.myrp1._tagKeys WHERE _name =~ /c.*/`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM mydb.myrp1./c.*/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0 FROM mydb.myrp1./c.*/`,
-			s:    `SELECT tagKey FROM mydb.myrp1._tagKeys WHERE _name =~ /c.*/`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM mydb.myrp1./c.*/`,
 		},
 		{
 			stmt: `SHOW TAG KEYS FROM mydb.myrp1.cpu WHERE region = 'uswest'`,
-			s:    `SELECT tagKey FROM mydb.myrp1._tagKeys WHERE (_name = 'cpu') AND (region = 'uswest')`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM mydb.myrp1.cpu WHERE region = 'uswest'`,
 		},
 		{
 			stmt: `SHOW TAG KEYS ON db0 FROM mydb.myrp1.cpu WHERE region = 'uswest'`,
-			s:    `SELECT tagKey FROM mydb.myrp1._tagKeys WHERE (_name = 'cpu') AND (region = 'uswest')`,
+			s:    `SELECT distinct(_tagKey) AS tagKey FROM mydb.myrp1.cpu WHERE region = 'uswest'`,
 		},
 		{
 			stmt: `SELECT value FROM cpu`,

query/emitter.go

@@ -20,6 +20,9 @@ type Emitter struct {
 	// The columns to attach to each row.
 	Columns []string
 
+	// Overridden measurement name to emit.
+	EmitName string
+
 	// The time zone location.
 	Location *time.Location
 
@@ -139,6 +142,10 @@ func (e *Emitter) loadBuf() (t int64, name string, tags Tags, err error) {
 
 // createRow creates a new row attached to the emitter.
 func (e *Emitter) createRow(name string, tags Tags, values []interface{}) {
+	if e.EmitName != "" {
+		name = e.EmitName
+	}
+
 	e.tags = tags
 	e.row = &models.Row{
 		Name:    name,