Github user wgtmac commented on a diff in the pull request:
https://github.com/apache/orc/pull/245#discussion_r180959089
--- Diff: site/_docs/encodings.md ---
@@ -123,6 +127,41 @@ DIRECT_V2 | PRESENT | Yes | Boolean
RLE
| DATA | No | Unbounded base 128 varints
| SECONDARY | No | Unsigned Integer RLE v2
+In ORC 2.0, DECIMAL and DECIMAL_V2 encodings are introduced and scale
+stream is totally removed as all decimal values use the same scale.
+There are two difference cases: precision<=18 and precision>18.
+
+### Decimal Encoding for precision <= 18
+
+When precision is no greater than 18, decimal values can be fully
+represented by 64-bit signed integers which are stored in DATA stream
+and use signed integer RLE.
+
+Encoding | Stream Kind | Optional | Contents
+:------------ | :-------------- | :------- | :-------
+DECIMAL | PRESENT | Yes | Boolean RLE
+ | DATA | No | Signed Integer RLE v1
+DECIMAL_V2 | PRESENT | Yes | Boolean RLE
+ | DATA | No | Signed Integer RLE v2
--- End diff --
For decimals, current Integer RLE will be used. As you have explained, I
agree that we should not use old RLE v1.
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