From 6534ce843f8765d42ac52ca9c7719a1d5ec27941 Mon Sep 17 00:00:00 2001
From: Tobias Guggenmos <tguggenm@redhat.com>
Date: Thu, 9 Jan 2020 18:36:13 +0100
Subject: [PATCH] PromQL: Use a sync.Pool for the generated parser structure
 (#6591)

* PromQL: Use a sync.Pool for the generated parser structure

The generated PromQL parser allocates a struct about 4kb in size on every run.

This puts a high load on the garbage collector.

To reduce that load, a sync.Pool is used to recycle these structures.

On small queries this makes parsing 2-3 times faster.

Signed-off-by: Tobias Guggenmos <tguggenm@redhat.com>
---
 promql/parse.go | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/promql/parse.go b/promql/parse.go
index 07feac875..c9d9af408 100644
--- a/promql/parse.go
+++ b/promql/parse.go
@@ -19,6 +19,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/pkg/errors"
@@ -28,8 +29,14 @@ import (
 	"github.com/prometheus/prometheus/util/strutil"
 )
 
+var parserPool = sync.Pool{
+	New: func() interface{} {
+		return &parser{}
+	},
+}
+
 type parser struct {
-	lex *Lexer
+	lex Lexer
 
 	inject    ItemType
 	injecting bool
@@ -54,7 +61,7 @@ func (e *ParseErr) Error() string {
 // ParseExpr returns the expression parsed from the input.
 func ParseExpr(input string) (expr Expr, err error) {
 	p := newParser(input)
-
+	defer parserPool.Put(p)
 	defer p.recover(&err)
 
 	expr = p.parseGenerated(START_EXPRESSION).(Expr)
@@ -66,6 +73,7 @@ func ParseExpr(input string) (expr Expr, err error) {
 // ParseMetric parses the input into a metric
 func ParseMetric(input string) (m labels.Labels, err error) {
 	p := newParser(input)
+	defer parserPool.Put(p)
 	defer p.recover(&err)
 
 	return p.parseGenerated(START_METRIC).(labels.Labels), nil
@@ -75,6 +83,7 @@ func ParseMetric(input string) (m labels.Labels, err error) {
 // label matchers.
 func ParseMetricSelector(input string) (m []*labels.Matcher, err error) {
 	p := newParser(input)
+	defer parserPool.Put(p)
 	defer p.recover(&err)
 
 	return p.parseGenerated(START_METRIC_SELECTOR).(*VectorSelector).LabelMatchers, nil
@@ -82,8 +91,14 @@ func ParseMetricSelector(input string) (m []*labels.Matcher, err error) {
 
 // newParser returns a new parser.
 func newParser(input string) *parser {
-	p := &parser{
-		lex: Lex(input),
+	p := parserPool.Get().(*parser)
+
+	p.injecting = false
+
+	// Clear lexer struct before reusing.
+	p.lex = Lexer{
+		input: input,
+		state: lexStatements,
 	}
 	return p
 }
@@ -112,6 +127,7 @@ func parseSeriesDesc(input string) (labels labels.Labels, values []sequenceValue
 	p := newParser(input)
 	p.lex.seriesDesc = true
 
+	defer parserPool.Put(p)
 	defer p.recover(&err)
 
 	result := p.parseGenerated(START_SERIES_DESCRIPTION).(*seriesDescription)