diff --git a/README.md b/README.md
index 2af0c8e..23c535d 100644
--- a/README.md
+++ b/README.md
@@ -111,12 +111,15 @@ pglite4j/
 
 - [ ] **Only `memory://` is supported** — no persistent / file-backed databases yet
 - [ ] **Single connection only** — PGlite is single-threaded; connection pool max size must be 1
-- [ ] **CMA buffer size is fixed** — large messages that exceed the CMA buffer (~12 MB total, ~16 KB per single message) are not yet handled via the file transport fallback
 - [ ] **Limited extensions** — only `plpgsql` and `dict_snowball` are bundled; adding more requires rebuilding the WASM binary
 - [ ] **Startup time** — first connection has some overhead it can be optimized more
 - [ ] **Binary size** — the WASM binary + pgdata resources add several MBs to the classpath
 - [ ] **Error recovery** — `clear_error()` integration for automatic transaction recovery is not yet wired up
 
+### CMA (Contiguous Memory Allocator)
+
+CMA is a preallocated contiguous region at the start of WASM linear memory used for zero-copy data transfer between Java and the PostgreSQL backend (similar concept to [Linux CMA](https://developer.toradex.com/software/linux-resources/linux-features/contiguous-memory-allocator-cma-linux/)). Messages that fit within the CMA buffer (default 12 MB) are transferred directly via shared memory. For responses that exceed the CMA buffer, the C code automatically falls back to file-based transport (`/pgdata/.s.PGSQL.5432.out`), which the Java side reads transparently.
+
 ## Building from source
 
 ```bash
diff --git a/core/pom.xml b/core/pom.xml
index 5d73321..31264c3 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -72,12 +72,15 @@
               <name>io.roastedroot.pglite4j.core.PGLiteModule</name>
               <wasmFile>../wasm-build/output/pglite.wasi</wasmFile>
               <!-- <interpreterFallback>WARN</interpreterFallback> -->
-              <!-- DEBUG: false -->
               <interpretedFunctions>
-                <function>5708</function>
-                <function>11479</function>
-                <function>17648</function>
-                <function>25134</function>
+                <function>2918</function>
+                <function>4335</function>
+                <function>4336</function>
+                <function>4494</function>
+                <function>4551</function>
+                <function>6394</function>
+                <function>6397</function>
+                <function>11038</function>
               </interpretedFunctions>
             </configuration>
           </execution>
diff --git a/core/src/main/java/io/roastedroot/pglite4j/core/PGLite.java b/core/src/main/java/io/roastedroot/pglite4j/core/PGLite.java
index 9108551..b813d4f 100644
--- a/core/src/main/java/io/roastedroot/pglite4j/core/PGLite.java
+++ b/core/src/main/java/io/roastedroot/pglite4j/core/PGLite.java
@@ -5,7 +5,6 @@
 import com.dylibso.chicory.runtime.Instance;
 import com.dylibso.chicory.wasi.WasiOptions;
 import com.dylibso.chicory.wasi.WasiPreview1;
-import com.dylibso.chicory.wasm.types.MemoryLimits;
 import io.roastedroot.zerofs.Configuration;
 import io.roastedroot.zerofs.ZeroFs;
 import java.io.BufferedReader;
@@ -87,7 +86,6 @@ private PGLite() {
                             .withImportValues(imports)
                             .withMachineFactory(PGLiteModule::create)
                             .withStart(false)
-                            .withMemoryLimits(new MemoryLimits(2571))
                             .build();
             this.exports = new PGLite_ModuleExports(this.instance);
 
@@ -127,6 +125,11 @@ public byte[] execProtocolRaw(byte[] message) {
         return concat(replies);
     }
 
+    /** Returns the CMA buffer size in bytes (for diagnostics / testing). */
+    public int getBufferSize() {
+        return exports.getBufferSize(0);
+    }
+
     public static Builder builder() {
         return new Builder();
     }
@@ -170,7 +173,34 @@ private byte[] wireRecvCma() {
         return resp;
     }
 
+    private byte[] wireRecvFile() {
+        try {
+            Path outFile = fs.getPath("/pgdata/.s.PGSQL.5432.out");
+            if (!Files.exists(outFile)) {
+                return null;
+            }
+            byte[] resp = Files.readAllBytes(outFile);
+            Files.delete(outFile);
+            exports.interactiveWrite(0);
+            pendingWireLen = 0;
+            return resp;
+        } catch (IOException e) {
+            throw new RuntimeException("Failed to read file transport output", e);
+        }
+    }
+
     private boolean collectReply(List<byte[]> replies) {
+        // Check channel: negative means C code fell back to file transport.
+        // Must check BEFORE wireRecvCma() since interactiveRead() would
+        // consume the read signal even when data went to file.
+        if (exports.getChannel() < 0) {
+            byte[] resp = wireRecvFile();
+            if (resp != null) {
+                replies.add(resp);
+                return true;
+            }
+            return false;
+        }
         byte[] resp = wireRecvCma();
         if (resp != null) {
             replies.add(resp);
diff --git a/core/src/test/java/io/roastedroot/pglite4j/core/PGLiteTest.java b/core/src/test/java/io/roastedroot/pglite4j/core/PGLiteTest.java
index a0937cd..233d942 100644
--- a/core/src/test/java/io/roastedroot/pglite4j/core/PGLiteTest.java
+++ b/core/src/test/java/io/roastedroot/pglite4j/core/PGLiteTest.java
@@ -68,6 +68,40 @@ public void createTableAndInsert() {
         }
     }
 
+    @Test
+    public void cmaBufferOverflow() {
+        try (PGLite pg = PGLite.builder().build()) {
+            doHandshake(pg);
+
+            int bufSize = pg.getBufferSize();
+            System.out.println(
+                    "CMA buffer size: " + bufSize + " bytes (" + (bufSize / 1024) + " KB)");
+
+            // Generate a wire protocol response that exceeds the CMA buffer.
+            // repeat('x', N) returns an N-byte string in the DataRow message.
+            int repeatLen = bufSize + 1000;
+            String sql = "SELECT repeat('x', " + repeatLen + ");";
+            System.out.println("Query: SELECT repeat('x', " + repeatLen + ")");
+
+            byte[] result = pg.execProtocolRaw(PgWireCodec.queryMessage(sql));
+            System.out.println("Response length: " + result.length + " bytes");
+            assertNotNull(result);
+            // The response must contain the full string + wire protocol overhead
+            assertTrue(
+                    result.length > repeatLen,
+                    "Expected response > " + repeatLen + " but got " + result.length);
+            assertTrue(
+                    PgWireCodec.hasReadyForQuery(result),
+                    "Expected ReadyForQuery in overflow response");
+
+            // Verify a normal query still works after the overflow
+            byte[] r2 = pg.execProtocolRaw(PgWireCodec.queryMessage("SELECT 42;"));
+            String data = PgWireCodec.parseDataRows(r2);
+            System.out.println("Post-overflow query: SELECT 42 => " + data);
+            assertTrue(data.contains("42"), "Normal query should work after CMA overflow");
+        }
+    }
+
     static void doHandshake(PGLite pg) {
         byte[] startup = PgWireCodec.startupMessage("postgres", "template1");
         byte[] resp1 = pg.execProtocolRaw(startup);
diff --git a/jdbc/src/test/java/io/roastedroot/pglite4j/jdbc/PgLiteDriverTest.java b/jdbc/src/test/java/io/roastedroot/pglite4j/jdbc/PgLiteDriverTest.java
index c23fa5e..04a8264 100644
--- a/jdbc/src/test/java/io/roastedroot/pglite4j/jdbc/PgLiteDriverTest.java
+++ b/jdbc/src/test/java/io/roastedroot/pglite4j/jdbc/PgLiteDriverTest.java
@@ -135,6 +135,22 @@ void selectWithWhere() throws SQLException {
 
     @Test
     @Order(8)
+    void largeResultSet() throws SQLException {
+        try (Statement stmt = connection.createStatement();
+                ResultSet rs =
+                        stmt.executeQuery(
+                                "SELECT n, repeat('x', 100) AS data"
+                                        + " FROM generate_series(1, 500) AS n")) {
+            int count = 0;
+            while (rs.next()) {
+                count++;
+            }
+            assertEquals(500, count);
+        }
+    }
+
+    @Test
+    @Order(9)
     void driverAcceptsUrl() throws SQLException {
         PgLiteDriver driver = new PgLiteDriver();
         assertTrue(driver.acceptsURL("jdbc:pglite:memory://"));
diff --git a/wasm-build/Makefile b/wasm-build/Makefile
index 08b9394..da202ad 100644
--- a/wasm-build/Makefile
+++ b/wasm-build/Makefile
@@ -6,7 +6,7 @@ WASM_FILE := $(OUTPUT_DIR)/pglite.wasi
 
 .PHONY: build clean unpack
 
-WASM_OPT_FLAGS ?= -Oz --strip-debug
+WASM_OPT_FLAGS ?= -O3 --strip-debug
 
 build:
 	WASM_OPT_FLAGS="$(WASM_OPT_FLAGS)" $(SCRIPT_DIR)build.sh
diff --git a/wasm-build/build.sh b/wasm-build/build.sh
index 65ce1f1..4edfb54 100755
--- a/wasm-build/build.sh
+++ b/wasm-build/build.sh
@@ -38,11 +38,12 @@ docker run --rm \
     -v "${OUTPUT_DIR}/sdk-dist:/tmp/sdk/dist:rw" \
     -v "${OUTPUT_DIR}/pglite:/tmp/pglite:rw" \
     -v "${OUTPUT_DIR}/pgdata:/pgdata:rw" \
+    -e CMA_MB="${CMA_MB:-12}" \
     -e DEBUG="${DEBUG:-true}" \
     -e PG_VERSION="${PG_VERSION:-17.5}" \
     -e PG_BRANCH="${PG_BRANCH:-REL_17_5_WASM-pglite}" \
     -e CI="${CI:-true}" \
-    -e WASM_OPT_FLAGS="${WASM_OPT_FLAGS:--Oz --strip-debug}" \
+    -e WASM_OPT_FLAGS="${WASM_OPT_FLAGS:--O3 --strip-debug}" \
     "${IMAGE_NAME}"
 
 echo "
diff --git a/wasm-build/docker/entrypoint.sh b/wasm-build/docker/entrypoint.sh
index 2c28e99..3de9780 100755
--- a/wasm-build/docker/entrypoint.sh
+++ b/wasm-build/docker/entrypoint.sh
@@ -13,7 +13,7 @@ export ZIC=${ZIC:-/usr/sbin/zic}
 export GETZIC=${GETZIC:-false}
 export WASI=true
 export CI=${CI:-true}
-export CMA_MB=${CMA_MB:-2}
+export CMA_MB=${CMA_MB:-12}
 export PGCRYPTO=${PGCRYPTO:-false}
 export NATIVE=${NATIVE:-false}
 export CONTAINER_PATH=""
diff --git a/wasm-build/patches/pglite-wasm/build.sh.diff b/wasm-build/patches/pglite-wasm/build.sh.diff
index 4a2b0f2..a6d0f59 100644
--- a/wasm-build/patches/pglite-wasm/build.sh.diff
+++ b/wasm-build/patches/pglite-wasm/build.sh.diff
@@ -18,7 +18,7 @@
          else
              echo "compilation of libpglite ${BUILD} support failed"
          fi
-@@ -114,8 +114,91 @@
+@@ -114,8 +114,103 @@
  
          if [ -f ${PG_DIST}/pglite.wasi ]
          then
@@ -103,6 +103,18 @@
 +            echo "wasi-vfs pack output:"
 +            ls -lh ${PG_DIST}/pglite-packed.wasi
 +            mv ${PG_DIST}/pglite-packed.wasi ${PG_DIST}/pglite.wasi
++
++            echo "=== running wasm-opt ${WASM_OPT_FLAGS} ==="
++            ls -lh ${PG_DIST}/pglite.wasi
++            wasm-opt ${WASM_OPT_FLAGS} ${PG_DIST}/pglite.wasi -o ${PG_DIST}/pglite-opt.wasi
++            OPT_RC=$?
++            if [ $OPT_RC -ne 0 ] || [ ! -s ${PG_DIST}/pglite-opt.wasi ]; then
++                echo "FATAL: wasm-opt failed (exit code $OPT_RC)"
++                exit 1
++            fi
++            mv ${PG_DIST}/pglite-opt.wasi ${PG_DIST}/pglite.wasi
++            echo "wasm-opt output:"
++            ls -lh ${PG_DIST}/pglite.wasi
 +
              cp ${PG_DIST}/pglite.wasi ${PGROOT}/bin/
              touch ${PGROOT}/bin/initdb ${PGROOT}/bin/postgres