diff --git a/src/config.ts b/src/config.ts
index cce1ce2..246bf5a 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -144,9 +144,25 @@ const Conf = {
   local(path: string): string {
     return mergePaths(Conf.localDomain, path);
   },
+  /** URL to send Sentry errors to. */
   get sentryDsn() {
     return Deno.env.get('SENTRY_DSN');
   },
+  /** SQLite settings. */
+  sqlite: {
+    /**
+     * Number of bytes to use for memory-mapped IO.
+     * https://www.sqlite.org/pragma.html#pragma_mmap_size
+     */
+    get mmapSize(): number {
+      const value = Deno.env.get('SQLITE_MMAP_SIZE');
+      if (value) {
+        return Number(value);
+      } else {
+        return 1024 * 1024 * 1024;
+      }
+    },
+  },
 };
 
 const optionalBooleanSchema = z
diff --git a/src/db.ts b/src/db.ts
index 43d7f04..99339a8 100644
--- a/src/db.ts
+++ b/src/db.ts
@@ -3,6 +3,7 @@ import path from 'node:path';
 
 import { DenoSqlite3, DenoSqliteDialect, FileMigrationProvider, Kysely, Migrator } from '@/deps.ts';
 import { Conf } from '@/config.ts';
+import { getPragma, setPragma } from '@/pragma.ts';
 
 interface DittoDB {
   events: EventRow;
@@ -61,6 +62,19 @@ const db = new Kysely<DittoDB>({
   }),
 });
 
+// Set PRAGMA values.
+await Promise.all([
+  setPragma(db, 'synchronous', 'normal'),
+  setPragma(db, 'temp_store', 'memory'),
+  setPragma(db, 'mmap_size', Conf.sqlite.mmapSize),
+]);
+
+// Log out PRAGMA values for debugging.
+['journal_mode', 'synchronous', 'temp_store', 'mmap_size'].forEach(async (pragma) => {
+  const value = await getPragma(db, pragma);
+  console.log(`PRAGMA ${pragma} = ${value};`);
+});
+
 const migrator = new Migrator({
   db,
   provider: new FileMigrationProvider({
diff --git a/src/db/migrations/008_wal.ts b/src/db/migrations/008_wal.ts
new file mode 100644
index 0000000..7f96226
--- /dev/null
+++ b/src/db/migrations/008_wal.ts
@@ -0,0 +1,9 @@
+import { Kysely, sql } from '@/deps.ts';
+
+export async function up(db: Kysely<any>): Promise<void> {
+  await sql`PRAGMA journal_mode = WAL`.execute(db);
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await sql`PRAGMA journal_mode = DELETE`.execute(db);
+}
diff --git a/src/pragma.ts b/src/pragma.ts
new file mode 100644
index 0000000..f5aa8e4
--- /dev/null
+++ b/src/pragma.ts
@@ -0,0 +1,15 @@
+import { type Kysely, sql } from '@/deps.ts';
+
+/** Set the PRAGMA and then read back its value to confirm. */
+function setPragma(db: Kysely<any>, pragma: string, value: string | number) {
+  return sql.raw(`PRAGMA ${pragma} = ${value}`).execute(db);
+}
+
+/** Get value of PRAGMA from the database. */
+async function getPragma(db: Kysely<any>, pragma: string) {
+  const result = await sql.raw(`PRAGMA ${pragma}`).execute(db);
+  const row = result.rows[0] as Record<string, unknown> | undefined;
+  return row?.[pragma];
+}
+
+export { getPragma, setPragma };