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Message Posted: Wed, 08 Apr 2015 @ 14:46:51 GMT


     
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Subj:   Re: Inserting/Updating same target table simultaneously by multiple sessions without locking
 
From:   Prescott, Kyle

You asking to update a table in a transactional fashion but via a mass insert/update from multiple concurrent sources/processes.

An Update DML statement (also insert and delete) that is from another table source with multiple rows involved will escalate any row-level write lock to an all-amp write lock as you cannot predict the data to be involved in the key lookup (containing to single-amp and row hash).

If you are really needing to do this in the fashion you describe, you will need to export the data to a file and import it through a BTEQ calling a query or macro (preferable) that will do this a row at a time and keep the locking isolated to the row hash. You can also do this with BTEQ with multiple sessions (or tpump/TPT stream) to accomplish this.

Easy BTEQ stub that logs on with 5 parallel sessions, imports a data file and uses multi-session updates through the macro to update the table. Also works better if the data is "not sorted" in row key order in the event your table is a NUPI defined vs. UPI and you have multiple rows to update within a row hash. In this case, the row hash lock could still block some transactions in the parallel process if the input is sorted by row hash.

     .SET SESSIONS 5;
     .LOGON DBC/USER,PSWD;
     .set quiet on;

     .REPEAT 5
        DATABASE ;

     .IMPORT file =  .REPEAT *
           Using (my_key integer,my_update_text char(50) )
           Exec update_it (:my_key, :my_update_text);

     .logoff;
     .quit;

Kyle Prescott
DBA Manager
Unum-GHDS
Chattanooga, TN



     
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