Delta length byte array encoding

README.md

@@ -182,7 +182,7 @@ Parquet encodings:
  - [X] BIT_PACKED
  - [X] DELTA_BINARY_PACKED
  - [X] DELTA_BYTE_ARRAY
- - [ ] DELTA_LENGTH_BYTE_ARRAY
+ - [X] DELTA_LENGTH_BYTE_ARRAY
  - [ ] BYTE_STREAM_SPLIT
 
 ## Hysnappy

src/datapageV2.js

@@ -1,5 +1,5 @@
 import { decompressPage } from './column.js'
-import { deltaBinaryUnpack, deltaByteArray } from './delta.js'
+import { deltaBinaryUnpack, deltaByteArray, deltaLengthByteArray } from './delta.js'
 import { readRleBitPackedHybrid, widthFromMaxInt } from './encoding.js'
 import { readPlain } from './plain.js'
 import { getMaxDefinitionLevel, getMaxRepetitionLevel } from './schema.js'
@@ -67,6 +67,9 @@ export function readDataPageV2(compressedBytes, ph, schemaPath, columnMetadata,
     const int32 = columnMetadata.type === 'INT32'
     dataPage = int32 ? new Int32Array(nValues) : new BigInt64Array(nValues)
     deltaBinaryUnpack(pageReader, nValues, dataPage)
+  } else if (daph2.encoding === 'DELTA_LENGTH_BYTE_ARRAY') {
+    dataPage = new Array(nValues)
+    deltaLengthByteArray(pageReader, nValues, dataPage)
   } else if (daph2.encoding === 'DELTA_BYTE_ARRAY') {
     dataPage = new Array(nValues)
     deltaByteArray(pageReader, nValues, dataPage)

src/delta.js

@@ -61,6 +61,20 @@ export function deltaBinaryUnpack(reader, nValues, output) {
   }
 }
 
+/**
+ * @param {DataReader} reader
+ * @param {number} nValues
+ * @param {Uint8Array[]} output
+ */
+export function deltaLengthByteArray(reader, nValues, output) {
+  const lengths = new Int32Array(nValues)
+  deltaBinaryUnpack(reader, nValues, lengths)
+  for (let i = 0; i < nValues; i++) {
+    output[i] = new Uint8Array(reader.view.buffer, reader.view.byteOffset + reader.offset, lengths[i])
+    reader.offset += lengths[i]
+  }
+}
+
 /**
  * @param {DataReader} reader
  * @param {number} nValues

test/files/delta_length_byte_array.metadata.json

@@ -0,0 +1,59 @@
+{
+  "version": 2,
+  "schema": [
+    {
+      "repetition_type": "REQUIRED",
+      "name": "schema",
+      "num_children": 1,
+      "field_id": -1
+    },
+    {
+      "type": "BYTE_ARRAY",
+      "repetition_type": "OPTIONAL",
+      "name": "FRUIT",
+      "converted_type": "UTF8",
+      "field_id": 1,
+      "logical_type": {
+        "type": "STRING"
+      }
+    }
+  ],
+  "num_rows": 1000,
+  "row_groups": [
+    {
+      "columns": [
+        {
+          "file_offset": 2629,
+          "meta_data": {
+            "type": "BYTE_ARRAY",
+            "encodings": [
+              "RLE",
+              "DELTA_LENGTH_BYTE_ARRAY"
+            ],
+            "path_in_schema": [
+              "FRUIT"
+            ],
+            "codec": "ZSTD",
+            "num_values": 1000,
+            "total_uncompressed_size": 23747,
+            "total_compressed_size": 2625,
+            "data_page_offset": 4,
+            "encoding_stats": [
+              {
+                "page_type": 3,
+                "encoding": "DELTA_LENGTH_BYTE_ARRAY",
+                "count": 1
+              }
+            ]
+          }
+        }
+      ],
+      "total_byte_size": 23747,
+      "num_rows": 1000,
+      "file_offset": 0,
+      "total_compressed_size": 2625,
+      "ordinal": 0
+    }
+  ],
+  "metadata_length": 105
+}