Make * and + non-greedy to double regex filter speed. (#4775)

* Optimize regular expressions in filters.

* Run original RE2 tests.

* Run both tests.

* Update pkg/logql/log/filter.go

Co-authored-by: Bryan Boreham <bjboreham@gmail.com>

* Update pkg/logql/log/filter.go

Co-authored-by: Bryan Boreham <bjboreham@gmail.com>

* Fix tests.

* Format code.

Co-authored-by: Bryan Boreham <bjboreham@gmail.com>

pkg/logql/log/filter.go

@@ -335,14 +335,34 @@ func parseRegexpFilter(re string, match bool) (Filterer, error) {
 	// attempt to improve regex with tricks
 	f, ok := simplify(reg)
 	if !ok {
-		return newRegexpFilter(re, match)
+		allNonGreedy(reg)
+		return newRegexpFilter(reg.String(), match)
 	}
 	if match {
 		return f, nil
 	}
 	return newNotFilter(f), nil
 }
 
+// allNonGreedy turns greedy quantifiers such as `.*` and `.+` into non-greedy ones. This is the same effect as writing
+// `.*?` and `.+?`. This is only safe because we use `Match`. If we were to find the exact position and length of the match
+// we would not be allowed to make this optimization. `Match` can return quicker because it is not looking for the longest match.
+// Prepending the expression with `(?U)` or passing `NonGreedy` to the expression compiler is not enough since it will
+// just negate `.*` and `.*?`.
+func allNonGreedy(regs ...*syntax.Regexp) {
+	clearCapture(regs...)
+	for _, re := range regs {
+		switch re.Op {
+		case syntax.OpCapture, syntax.OpConcat, syntax.OpAlternate:
+			allNonGreedy(re.Sub...)
+		case syntax.OpStar, syntax.OpPlus:
+			re.Flags = re.Flags | syntax.NonGreedy
+		default:
+			continue
+		}
+	}
+}
+
 // simplify a regexp expression by replacing it, when possible, with a succession of literal filters.
 // For example `(foo|bar)` will be replaced by  `containsFilter(foo) or containsFilter(bar)`
 func simplify(reg *syntax.Regexp) (Filterer, bool) {

pkg/logql/log/filter_test.go

@@ -55,19 +55,19 @@ func Test_SimplifiedRegex(t *testing.T) {
 		{"(?i)foo", true, newContainsFilter([]byte("foo"), true), true},
 
 		// regex we are not supporting.
-		{"[a-z]+foo", false, nil, false},
-		{".+foo", false, nil, false},
-		{".*fo.*o", false, nil, false},
-		{`\d`, false, nil, false},
-		{`\sfoo`, false, nil, false},
+		{"[a-z]+foo", true, nil, false},
+		{".+foo", true, nil, false},
+		{".*fo.*o", true, nil, false},
+		{`\d`, true, nil, false},
+		{`\sfoo`, true, nil, false},
 		{`foo?`, false, nil, false},
-		{`foo{1,2}bar{2,3}`, false, nil, false},
-		{`foo|\d*bar`, false, nil, false},
-		{`foo|fo{1,2}`, false, nil, false},
-		{`foo|fo\d*`, false, nil, false},
-		{`foo|fo\d+`, false, nil, false},
-		{`(\w\d+)`, false, nil, false},
-		{`.*f.*oo|fo{1,2}`, false, nil, false},
+		{`foo{1,2}bar{2,3}`, true, nil, false},
+		{`foo|\d*bar`, true, nil, false},
+		{`foo|fo{1,2}`, true, nil, false},
+		{`foo|fo\d*`, true, nil, false},
+		{`foo|fo\d+`, true, nil, false},
+		{`(\w\d+)`, true, nil, false},
+		{`.*f.*oo|fo{1,2}`, true, nil, false},
 	} {
 		t.Run(test.re, func(t *testing.T) {
 			d, err := newRegexpFilter(test.re, test.match)
@@ -83,7 +83,9 @@ func Test_SimplifiedRegex(t *testing.T) {
 			}
 			// otherwise ensure we have different filter
 			require.NotEqual(t, f, d)
-			require.Equal(t, test.expected, f)
+			if test.expected != nil {
+				require.Equal(t, test.expected, f)
+			}
 			// tests all lines with both filter, they should have the same result.
 			for _, line := range fixtures {
 				l := []byte(line)