diff --git a/package.json b/package.json
index d889ed8..21c77e8 100644
--- a/package.json
+++ b/package.json
@@ -45,7 +45,7 @@
     "test": "vitest run"
   },
   "dependencies": {
-    "hyparquet": "1.12.0"
+    "hyparquet": "1.12.1"
   },
   "devDependencies": {
     "@babel/eslint-parser": "7.27.0",
diff --git a/src/bytewriter.js b/src/bytewriter.js
index 6850ce0..9124334 100644
--- a/src/bytewriter.js
+++ b/src/bytewriter.js
@@ -8,8 +8,9 @@
  */
 export function ByteWriter() {
   this.buffer = new ArrayBuffer(1024)
-  this.offset = 0
   this.view = new DataView(this.buffer)
+  this.offset = 0 // bytes written
+  this.index = 0 // index in buffer
   return this
 }
 
@@ -18,8 +19,8 @@ export function ByteWriter() {
  */
 ByteWriter.prototype.ensure = function(size) {
   // auto-expanding buffer
-  if (this.offset + size > this.buffer.byteLength) {
-    const newSize = Math.max(this.buffer.byteLength * 2, this.offset + size)
+  if (this.index + size > this.buffer.byteLength) {
+    const newSize = Math.max(this.buffer.byteLength * 2, this.index + size)
     const newBuffer = new ArrayBuffer(newSize)
     // TODO: save buffers until later and merge once?
     new Uint8Array(newBuffer).set(new Uint8Array(this.buffer))
@@ -32,61 +33,67 @@ ByteWriter.prototype.finish = function() {
 }
 
 ByteWriter.prototype.getBuffer = function() {
-  return this.buffer.slice(0, this.offset)
+  return this.buffer.slice(0, this.index)
 }
 
 /**
  * @param {number} value
  */
 ByteWriter.prototype.appendUint8 = function(value) {
-  this.ensure(this.offset + 1)
-  this.view.setUint8(this.offset, value)
+  this.ensure(this.index + 1)
+  this.view.setUint8(this.index, value)
   this.offset++
+  this.index++
 }
 
 /**
  * @param {number} value
  */
 ByteWriter.prototype.appendUint32 = function(value) {
-  this.ensure(this.offset + 4)
-  this.view.setUint32(this.offset, value, true)
+  this.ensure(this.index + 4)
+  this.view.setUint32(this.index, value, true)
   this.offset += 4
+  this.index += 4
 }
 
 /**
  * @param {number} value
  */
 ByteWriter.prototype.appendInt32 = function(value) {
-  this.ensure(this.offset + 4)
-  this.view.setInt32(this.offset, value, true)
+  this.ensure(this.index + 4)
+  this.view.setInt32(this.index, value, true)
   this.offset += 4
+  this.index += 4
 }
 
 /**
  * @param {bigint} value
  */
 ByteWriter.prototype.appendInt64 = function(value) {
-  this.ensure(this.offset + 8)
-  this.view.setBigInt64(this.offset, BigInt(value), true)
+  this.ensure(this.index + 8)
+  this.view.setBigInt64(this.index, BigInt(value), true)
   this.offset += 8
+  this.index += 8
 }
 
 /**
  * @param {number} value
  */
 ByteWriter.prototype.appendFloat32 = function(value) {
-  this.ensure(this.offset + 8)
-  this.view.setFloat32(this.offset, value, true)
+  this.ensure(this.index + 8)
+  this.view.setFloat32(this.index, value, true)
   this.offset += 4
+  this.index += 4
 }
 
 /**
  * @param {number} value
  */
 ByteWriter.prototype.appendFloat64 = function(value) {
-  this.ensure(this.offset + 8)
-  this.view.setFloat64(this.offset, value, true)
+  this.ensure(this.index + 8)
+  this.view.setFloat64(this.index, value, true)
   this.offset += 8
+  this.index += 8
 }
 
 /**
@@ -100,9 +107,10 @@ ByteWriter.prototype.appendBuffer = function(value) {
  * @param {Uint8Array} value
  */
 ByteWriter.prototype.appendBytes = function(value) {
-  this.ensure(this.offset + value.length)
-  new Uint8Array(this.buffer, this.offset, value.length).set(value)
+  this.ensure(this.index + value.length)
+  new Uint8Array(this.buffer, this.index, value.length).set(value)
   this.offset += value.length
+  this.index += value.length
 }
 
 /**
diff --git a/src/column.js b/src/column.js
index 2388f26..7320c3e 100644
--- a/src/column.js
+++ b/src/column.js
@@ -64,7 +64,7 @@ export function writeColumn(writer, schemaPath, values, compressed, stats) {
     codec: compressed ? 'SNAPPY' : 'UNCOMPRESSED',
     num_values: BigInt(num_values),
     total_compressed_size: BigInt(writer.offset - offsetStart),
-    total_uncompressed_size: BigInt(writer.offset - offsetStart),
+    total_uncompressed_size: BigInt(writer.offset - offsetStart), // TODO
     data_page_offset,
     dictionary_page_offset,
     statistics,
diff --git a/src/filewriter.js b/src/filewriter.js
index 34a748f..ef01cb0 100644
--- a/src/filewriter.js
+++ b/src/filewriter.js
@@ -17,10 +17,10 @@ export function fileWriter(filename) {
   fs.writeFileSync(filename, '', { flag: 'w' })
 
   function flush() {
-    const chunk = writer.buffer.slice(0, writer.offset)
+    const chunk = writer.buffer.slice(0, writer.index)
     // TODO: async
     fs.writeFileSync(filename, new Uint8Array(chunk), { flag: 'a' })
-    writer.offset = 0
+    writer.index = 0
   }
 
   /**
@@ -28,11 +28,11 @@ export function fileWriter(filename) {
    * @param {number} size
    */
   writer.ensure = function(size) {
-    if (writer.offset > chunkSize) {
+    if (writer.index > chunkSize) {
       flush()
     }
-    if (writer.offset + size > writer.buffer.byteLength) {
-      const newSize = Math.max(writer.buffer.byteLength * 2, writer.offset + size)
+    if (writer.index + size > writer.buffer.byteLength) {
+      const newSize = Math.max(writer.buffer.byteLength * 2, writer.index + size)
       const newBuffer = new ArrayBuffer(newSize)
       new Uint8Array(newBuffer).set(new Uint8Array(writer.buffer))
       writer.buffer = newBuffer
diff --git a/src/metadata.js b/src/metadata.js
index ba21a1c..390c0e4 100644
--- a/src/metadata.js
+++ b/src/metadata.js
@@ -83,8 +83,10 @@ export function writeMetadata(writer, metadata) {
     field_6: metadata.created_by,
   }
 
+  // write metadata as thrift
   const metadataStart = writer.offset
   serializeTCompactProtocol(writer, compact)
+  // write metadata length
   const metadataLength = writer.offset - metadataStart
   writer.appendUint32(metadataLength)
 }
diff --git a/src/types.d.ts b/src/types.d.ts
index 810432a..bfb8f33 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -25,8 +25,9 @@ export interface ColumnData {
 
 export interface Writer {
   buffer: ArrayBuffer
-  offset: number
   view: DataView
+  offset: number
+
   ensure(size: number): void
   finish(): void
   getBuffer(): ArrayBuffer