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https://issues.apache.org/jira/browse/TRAFODION-2755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16190463#comment-16190463
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ASF GitHub Bot commented on TRAFODION-2755:
-------------------------------------------
Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/1247#discussion_r142537859
--- Diff: docs/lob_guide/src/asciidoc/_chapters/working_with_lob.adoc ---
@@ -751,4 +751,380 @@ CQD `LOB_MAX_SIZE` (default 10G expressed in M
[10000M]).
* Extract Target Locations
+
-The file to extract to can be a local linux file or a local HDFS file.
\ No newline at end of file
+The file to extract to can be a local linux file or a local HDFS file.
+
+[#deleting column from a sql table containing lob columns]
+== Deleting Column from a SQL Table Containing LOB columns
+
+[#syntax]
+=== Syntax
+
+```
+DELETE lob-column-name FROM table-name [WHERE CLAUSE]
+```
+
+[#considerations]
+=== Considerations
+
+When one or more rows containing LOB columns are deleted from LOB table,
only the metadata information is dropped and the hdfs data remains as it is.
The references to the lob data are removed from the lob descriptor file.
+
+This mechanism has not been implemented yet as a separate utility but it
is triggered as a part of insert, update and append operations. For more
information, see <<garbage collection,Garbage Collection>>.
+
+[#dropping a sql table containing lob columns ]
+== Dropping a SQL Table Containing LOB Columns
+
+Drop works like any other drop table. All dependent tables are deleted.
All files in hdfs (data and descriptor) files are also deleted.
+
+For more information, see <<drop_table_statement,DROP TABLE Statement>> in
http://trafodion.incubator.apache.org/docs/sql_reference/index.html[Trafodion
SQL Reference Manual].
+
+[#garbage collection]
+== Garbage Collection
+
+When a lob datafile for a column has reached a certain limit, defined by a
CQD `LOB_GC_LIMIT_SIZE`, then a compaction is triggered automatically. +
+The default GC Limit is 10GB and can be changed if needed.
+
+The need for GC arises because when a delete operation or an update
operation is performed, the old data black in the hdfs file will be left as
unused. +
+In the case of update, the old data will be left as unused and the new
data will be written into a new section, so all these “holes” in the LOB data
file are needlessly occupying space.
--- End diff --
Consider: "... and the new data will be written into a new section, leaving
"holes" in the LOB data file that needlessly take up space."
> Create *Trafodion SQL Large Objects Guide* 2
> --------------------------------------------
>
> Key: TRAFODION-2755
> URL: https://issues.apache.org/jira/browse/TRAFODION-2755
> Project: Apache Trafodion
> Issue Type: Documentation
> Reporter: Liu Yu
> Assignee: Liu Yu
>
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