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https://issues.apache.org/jira/browse/TRAFODION-2408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15795741#comment-15795741
]
ASF GitHub Bot commented on TRAFODION-2408:
-------------------------------------------
Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/889#discussion_r94451970
--- Diff: core/sql/executor/ExExeUtil.h ---
@@ -2970,8 +2970,92 @@ class ExExeUtilLobExtractTcb : public ExExeUtilTcb
LOBglobals *lobGlobals_;
};
+
+
+//////////////////////////////////////////////////////////////////////////
+// -----------------------------------------------------------------------
+// ExExeUtilLobUpdateTdb
+// -----------------------------------------------------------------------
+class ExExeUtilLobUpdateTdb : public ComTdbExeUtilLobUpdate
+{
+ public:
+
+ // ---------------------------------------------------------------------
+ // Constructor is only called to instantiate an object used for
+ // retrieval of the virtual table function pointer of the class while
+ // unpacking. An empty constructor is enough.
+ // ---------------------------------------------------------------------
+ NA_EIDPROC ExExeUtilLobUpdateTdb()
+ {}
+
+ NA_EIDPROC virtual ~ExExeUtilLobUpdateTdb()
+ {}
+
+
+ // ---------------------------------------------------------------------
+ // Build a TCB for this TDB. Redefined in the Executor project.
+ // ---------------------------------------------------------------------
+ NA_EIDPROC virtual ex_tcb *build(ex_globals *globals);
+private:
+};
+
+//////////////////////////////////////////////////////////////////////////
+// -----------------------------------------------------------------------
+// ExExeUtilLobUpdateTcb
+// -----------------------------------------------------------------------
+
+
+class ExExeUtilLobUpdateTcb : public ExExeUtilTcb
+{
+ friend class ExExeUtilLobUpdateTdb;
+ friend class ExExeUtilPrivateState;
+
+public:
+ // Constructor
+ ExExeUtilLobUpdateTcb(const ComTdbExeUtilLobUpdate & exe_util_tdb,
+ const ex_tcb * child_tcb,
+ ex_globals * glob = 0);
+
+ virtual short work();
+
+ ExExeUtilLobUpdateTdb & lobTdb() const
+ {
+ return (ExExeUtilLobUpdateTdb &) tdb;
+ };
+ LOBglobals *getLobGlobals() { return lobGlobals_;}
+ protected:
+ enum Step
+ {
+ EMPTY_,
+ GET_HANDLE_,
+ UPDATE_LOB_DATA_,
+ EMPTY_LOB_DATA_,
+ APPEND_LOB_DATA_,
+ RETURN_STATUS_,
+ DONE_,
+ CANCEL_,
+ HANDLE_ERROR_,
+ CANCELLED_
+ };
+ Step step_;
+ Lng32 lobHandleLen_;
+ char lobHandle_[2050];
--- End diff --
How are the lengths of these variables derived?
> Support for empty_blob() and update syntax using lobhandle
> ----------------------------------------------------------
>
> Key: TRAFODION-2408
> URL: https://issues.apache.org/jira/browse/TRAFODION-2408
> Project: Apache Trafodion
> Issue Type: Sub-task
> Components: sql-exe
> Reporter: Sandhya Sundaresan
> Assignee: Sandhya Sundaresan
>
> This subtask in SQL is to help JDBC implementation for LOBs. They require the
> eimplementation of 2 interfaces
> .EMPTY_BLOB() , EMPTY_CLOB()
> update done directly to a lobhandle . This update syntax is different form
> the regular updates to lob columns using position.
> Assume a lob table of type :
> Create table tlob(c1 int , c2 blob, primary key (c1));
> Insert :
> Insert into tlob values (1, empty_blob());
> Insert into tlob values (1,empty_clob());
>
>
> This will create a lob handle . It will also create an empty descriptor
> handle entry and 1 chunk in the descriptor chunks table that is of size 0.
>
> The “type” of the lob handle will be the same as the underlying lob type of
> the column.
>
> Eg if we had created the table to hold external lobs
> Create table tlob(c1 int , c2 blob storage ‘external’ , primary key
> (c1));
> Insert into tlob values (1, empty_blob());
>
> The lob handle for this tlobext will contain the type ‘8’ instead of ‘2’ (as
> is the case for tlob.)
>
> But looking at the lob handle you will not be able to say if it’s empty or
> not. But if lob data is selected out it will be empty.
>
> Update:
> Assume tlob has some lob data in it.
>
> Update tlob set c2=empty_blob();
> This will replace all lob data in the table with the empty lob.
> The lob handle remains the same as before.
>
> Update tlob set c2 = stringtolob(‘xxxx’);
> This will replace the empty lob entry inth
> descriptor handle and descriptor chunks table with a new entry.
> OR
> Update tlob set c2 – stringtolob(‘xxxx’, append);
> This will append the new data to the empty lob. So
> it will leave 2 entries in the descriptor handle and descriptor chunks table.
>
> But the result when you select the data will be the same in both cases
> above.
>
>
> Update directly using a lobhandle using a buffer programmatically :
> New syntax has been introduced to allow updating a lob entry using lob
> handle directory. This is not positional syntax.
>
> The syntax is as follows :
>
> update lob (LOB ‘<lob handle>’, LOCATION < int64 address>, SIZE <
> int64 size>);
> This will take a lob handle as input (it could be an empty lob or have
> existing data). It will replace the contents with the data specified in
> LOCATION.
>
> update lob (LOB ‘<lob handle>’, LOCATION < int64 address>, SIZE <
> int64 size>, APPEND);
> This will take a lob handle as input (it could be an empty lob or have
> existing data). It will append the contents with the data specified in
> LOCATION.
>
> update lob (LOB ‘<lob handle>’, TRUNCATE);
> This will truncate the existing data and initialize the lob to empty_lob
> for the provided lob handle.
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