Squashed 'backend/go-sqlite3/' content from commit 20826e8

git-subtree-dir: backend/go-sqlite3
git-subtree-split: 20826e87d8f061d0a7266562f43950ee06e2e9c0

sqlite3_stmt_cache_bench_test.go

@@ -0,0 +1,88 @@
+// Copyright (C) 2019 Yasuhiro Matsumoto <mattn.jp@gmail.com>.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+//go:build cgo
+// +build cgo
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql/driver"
+	"fmt"
+	"testing"
+)
+
+// BenchmarkStmtCache measures the stmt cache hit / miss / eviction paths by
+// cycling through a fixed set of queries under various cache sizes. It is
+// intended for comparing cache behavior changes, not for absolute numbers.
+func BenchmarkStmtCache(b *testing.B) {
+	cases := []struct {
+		name      string
+		cacheSize int
+		keyCount  int
+	}{
+		{"off", 0, 1},                 // baseline: no cache
+		{"size4_keys1_hit", 4, 1},     // trivial hit path
+		{"size4_keys4_hit", 4, 4},     // all queries fit, always hit
+		{"size4_keys8_evict", 4, 8},   // working set > cache: miss + eviction
+		{"size16_keys8_hit", 16, 8},   // all queries fit in larger cache
+		{"size16_keys32_evict", 16, 32}, // working set >> cache
+	}
+	for _, tc := range cases {
+		b.Run(tc.name, func(b *testing.B) {
+			dsn := ":memory:"
+			if tc.cacheSize > 0 {
+				dsn = fmt.Sprintf(":memory:?_stmt_cache_size=%d", tc.cacheSize)
+			}
+			d := SQLiteDriver{}
+			conn, err := d.Open(dsn)
+			if err != nil {
+				b.Fatal(err)
+			}
+			defer conn.Close()
+			c := conn.(*SQLiteConn)
+
+			queries := make([]string, tc.keyCount)
+			for i := range queries {
+				// Distinct literal forces a distinct prepared statement.
+				queries[i] = fmt.Sprintf("SELECT %d", i+1)
+			}
+
+			ctx := context.Background()
+			// Warm up: exercise each query at least once so the cache (if any)
+			// reaches steady state before timing begins.
+			for _, q := range queries {
+				rows, err := c.query(ctx, q, nil)
+				if err != nil {
+					b.Fatal(err)
+				}
+				drainRows(b, rows)
+			}
+
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				q := queries[i%len(queries)]
+				rows, err := c.query(ctx, q, nil)
+				if err != nil {
+					b.Fatal(err)
+				}
+				drainRows(b, rows)
+			}
+		})
+	}
+}
+
+func drainRows(b *testing.B, rows driver.Rows) {
+	b.Helper()
+	dest := make([]driver.Value, len(rows.Columns()))
+	for {
+		if err := rows.Next(dest); err != nil {
+			break
+		}
+	}
+	rows.Close()
+}