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new 861ba2e [CARBONDATA-4185] Doc Changes for Heterogeneous format
segments in carbondata
861ba2e is described below
commit 861ba2e44f8087e15fbdba278e21e229355b7d99
Author: Mahesh Raju Somalaraju <[email protected]>
AuthorDate: Wed May 12 23:11:57 2021 +0530
[CARBONDATA-4185] Doc Changes for Heterogeneous format segments in
carbondata
Why is this PR needed?
Heterogeneous format segments in carbondata documenation.
What changes were proposed in this PR?
Add segment feature background and impact on existed carbondata features
This closes #4134
---
README.md | 1 +
docs/addsegment-guide.md | 78 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 79 insertions(+)
diff --git a/README.md b/README.md
index 4f8da5c..d1b47af 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,7 @@ CarbonData is built using Apache Maven, to [build
CarbonData](https://github.com
* [CarbonData Lucene
Index](https://github.com/apache/carbondata/blob/master/docs/index/lucene-index-guide.md)
* [CarbonData
MV](https://github.com/apache/carbondata/blob/master/docs/mv-guide.md)
* [Carbondata Secondary
Index](https://github.com/apache/carbondata/blob/master/docs/index/secondary-index-guide.md)
+* [Heterogeneous format segments in
carbondata](https://github.com/apache/carbondata/blob/master/docs/addsegment-guide.md)
* [SDK
Guide](https://github.com/apache/carbondata/blob/master/docs/sdk-guide.md)
* [C++ SDK
Guide](https://github.com/apache/carbondata/blob/master/docs/csdk-guide.md)
* [Performance
Tuning](https://github.com/apache/carbondata/blob/master/docs/performance-tuning.md)
diff --git a/docs/addsegment-guide.md b/docs/addsegment-guide.md
new file mode 100644
index 0000000..a45e6d6
--- /dev/null
+++ b/docs/addsegment-guide.md
@@ -0,0 +1,78 @@
+<!--
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to you under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+
+# Heterogeneous format segments in carbondata
+
+###Background
+In the industry, many users already adopted to data with different formats
like ORC, Parquet, JSON, CSV etc.,
+If users want to migrate to Carbondata for better performance or for better
features then there is no direct way.
+All the existing data needs to be converted to Carbondata to migrate.
+This solution works out if the existing data is less, what if the existing
data is more?
+Heterogeneous format segments aims to solve this problem by avoiding data
conversion.
+
+###Add segment with path and format
+Users can add the existing data as a segment to the carbon table provided the
schema of the data
+ and the carbon table should be the same.
+
+```
+Alter table table_name add segment options (‘path’=
'hdfs://usr/oldtable,'format'=parquet)
+```
+In the above command user can add the existing data to the carbon table as a
new segment and also
+ can provide the data format.
+
+During add segment, it will infer the schema from data and validates the
schema against the carbon table.
+If the schema doesn’t match it throws an exception.
+
+###Changes to tablestatus file
+Carbon adds the new segment by adding segment information to tablestatus file.
In order to add the path and format information to tablestatus, we are going to
add `segmentPath` and ‘format’ to the tablestatus file.
+And any extra `options` will be added to the segment file.
+
+
+###Changes to Spark Integration
+During select query carbon reads data through RDD which is created by
+ CarbonDatasourceHadoopRelation.buildScan, This RDD reads data from physical
carbondata files and provides data to spark query plan.
+To support multiple formats per segment basis we can create multiple RDD using
the existing Spark
+ file format scan class FileSourceScanExec . This class can generate scan RDD
for all spark supported formats. We can union all these multi-format RDD and
create a single RDD and provide it to spark query plan.
+
+Note: This integration will be clean as we use the sparks optimized reading,
pruning and it
+ involves whole codegen and vector processing with unsafe support.
+
+###Changes to Presto Integration
+CarbondataSplitManager can create the splits for carbon and as well as for
other formats and
+ choose the page source as per the split.
+
+### Impact on existed feature
+**Count(\*) query:** In case if the segments are mixed with different formats
then driver side
+ optimization for count(*) query will not work so it will be executed on
executor side.
+
+**Index DataMaps:** Datamaps like block/blocklet datamap will only work for
carbondata format
+ segments so there would not be any driver side pruning for other formats.
+
+**Update/Delete:** Update & Delete operations cannot be allowed on the table
which has mixed formats
+But it can be allowed if the external segments are added with carbondata
format.
+
+**Compaction:** The other format segments cannot be compacted but carbondata
segments inside that
+ table will be compacted.
+
+**Show Segments:** Now it shows the format and path of the segment along with
current information.
+
+**Delete Segments & Clean Files:** If the segment to be deleted is external
then it will not be
+ deleted physically. If the segment is present internally only will be deleted
physically.
+
+**MV DataMap:** These datamaps can be created on the mixed format table
without any
+ impact.
+
\ No newline at end of file
