Is PRAGMA mmap_size supported?

[lbe]

While working through some performance testing, I realized that I was not able to get PRAMA mmap_size assigned either from a URI DSN or from a direct query. Does go-sqlite3 support this pragma?

I created the following test program to show what I am doing and the results that I am seeing.

package main

import (
	"database/sql"
	"fmt"
	"log"
	"os"

	_ "github.com/ncruces/go-sqlite3/driver"
	_ "github.com/ncruces/go-sqlite3/embed"
)

func main() {
	// Test 1: mmap_size in URI DSN
	testDSNPragma()

	// Test 2: mmap_size set via SQL PRAGMA
	testSQLPragma()
}

func testDSNPragma() {
	dbPath := "test_dsn.db"
	os.Remove(dbPath)
	defer os.Remove(dbPath)

	dsn := fmt.Sprintf("file:%s?mmap_size=268435456", dbPath)
	db, err := sql.Open("sqlite3", dsn)
	if err != nil {
		log.Fatalf("Failed to open DB with DSN: %v", err)
	}
	defer db.Close()

	var mmapSize int64
	err = db.QueryRow("PRAGMA mmap_size").Scan(&mmapSize)
	if err != nil {
		log.Fatalf("Failed to query mmap_size: %v", err)
	}

	fmt.Printf("DSN Pragma Test - mmap_size: %d\n", mmapSize)
	switch mmapSize {
	case 268435456:
		fmt.Println("  Result: SUCCESS (value matches DSN setting)")
	case 0:
		fmt.Println("  Result: FAILED (mmap_size not set via DSN)")
	default:
		fmt.Println("  Result: PARTIAL (value set but different)")
	}
}

func testSQLPragma() {
	dbPath := "test_sql.db"
	os.Remove(dbPath)
	defer os.Remove(dbPath)

	dsn := fmt.Sprintf("file:%s", dbPath)
	db, err := sql.Open("sqlite3", dsn)
	if err != nil {
		log.Fatalf("Failed to open DB: %v", err)
	}
	defer db.Close()

	_, err = db.Exec("PRAGMA mmap_size = 268435456")
	if err != nil {
		log.Fatalf("Failed to set mmap_size via PRAGMA: %v", err)
	}

	var mmapSize int64
	err = db.QueryRow("PRAGMA mmap_size").Scan(&mmapSize)
	if err != nil {
		log.Fatalf("Failed to query mmap_size: %v", err)
	}

	fmt.Printf("\nSQL Pragma Test - mmap_size: %d\n", mmapSize)
	switch mmapSize {
	case 268435456:
		fmt.Println("  Result: SUCCESS (value matches PRAGMA setting)")
	case 0:
		fmt.Println("  Result: FAILED (mmap_size not set via PRAGMA)")
	default:
		fmt.Println("  Result: PARTIAL (value set but different)")
	}
}

The resulting output is:

sqlite-dbconnpool on 🍣 main [📝 🛤️ ] via 🐹 v1.26.0 via  14GiB/24GiB
[11:57:58] ➜  go run ./cmd/testNcrucesMmapSize/.
DSN Pragma Test - mmap_size: 0
  Result: FAILED (mmap_size not set via DSN)

SQL Pragma Test - mmap_size: 0
  Result: FAILED (mmap_size not set via PRAGMA)

I have searched the documentation, discussions, wiki and issues and not found anything. I noticed a couple of test cases that contain mmap_size but am too ignorant regarding wazero and WASM to know how to interpret them. I'm hopeful this means yes and I'm just doing something wrong.

Thanks in advance,

lbe

[ncruces]

No, SQLITE_MAX_MMAP_SIZE is set to zero.

Given the way Wasm sandbox works, and how much memory is available to it, it's hard to see a way to support it that actually improves performance.

[lbe]

Thank you for the quick confirmation