Github user xuchuanyin commented on a diff in the pull request:
https://github.com/apache/carbondata/pull/2590#discussion_r207084686
--- Diff: docs/data-management-on-carbondata.md ---
@@ -126,20 +126,33 @@ This tutorial is going to introduce all commands and
data operations on CarbonDa
- **Local Dictionary Configuration**
- Local Dictionary is generated only for no-dictionary string/varchar
datatype columns. It helps in:
+ Local Dictionary is generated only for string/varchar datatype
columns which are not included in dictionary include. It helps in:
1. Getting more compression on dimension columns with less
cardinality.
2. Filter queries and full scan queries on No-dictionary columns with
local dictionary will be faster as filter will be done on encoded data.
3. Reducing the store size and memory footprint as only unique values
will be stored as part of local dictionary and corresponding data will be
stored as encoded data.
-
- By default, Local Dictionary will be enabled and generated for all
no-dictionary string/varchar datatype columns.
+
+ **The cost for Local Dictionary:** The memory size will increase when
local dictionary is enabled.
+
+ **NOTE:** Following Data Types are not Supported for Local Dictionary:
+ * SMALLINT
+ * INTEGER
+ * BIGINT
+ * DOUBLE
+ * DECIMAL
+ * TIMESTAMP
+ * DATE
+ * CHAR
--- End diff --
Why is `CHAR` not supported? As I know, SparkSQL treat both varchar and
char as string, so in carbon data we actually see string.
---
