PARQUET-2222: Fix incorrect spec for RLE encoding of data page v2
This closes #193
diff --git a/Encodings.md b/Encodings.md
index a70ae6f..5e38d48 100644
--- a/Encodings.md
+++ b/Encodings.md
@@ -68,6 +68,7 @@
The grammar for this encoding looks like this, given a fixed bit-width known in advance:
```
rle-bit-packed-hybrid: <length> <encoded-data>
+// length is not always prepended, please check the table below for more detail
length := length of the <encoded-data> in bytes stored as 4 bytes little endian (unsigned int32)
encoded-data := <run>*
run := <bit-packed-run> | <rle-run>
@@ -123,6 +124,23 @@
* Dictionary indices
* Boolean values in data pages, as an alternative to PLAIN encoding
+Whether prepending the four-byte `length` to the `encoded-data` is summarized as the table below:
+```
++--------------+------------------------+-----------------+
+| Page kind | RLE-encoded data kind | Prepend length? |
++--------------+------------------------+-----------------+
+| Data page v1 | Definition levels | Y |
+| | Repetition levels | Y |
+| | Dictionary indices | N |
+| | Boolean values | Y |
++--------------+------------------------+-----------------+
+| Data page v2 | Definition levels | N |
+| | Repetition levels | N |
+| | Dictionary indices | N |
+| | Boolean values | Y |
++--------------+------------------------+-----------------+
+```
+
### <a name="BITPACKED"></a>Bit-packed (Deprecated) (BIT_PACKED = 4)
This is a bit-packed only encoding, which is deprecated and will be replaced by the [RLE/bit-packing](#RLE) hybrid encoding.
