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PODoes a MERGE INTO statement lock the entire table when merging into a partitioned table based on the partitioned columns?
 

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  1. PODoes a MERGE INTO statement lock the entire table when merging into a partitioned table based on the partitioned columns?
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    <p>After some performance issues occurred in our production environment, I asked for assistance from our database administrators. While helping, they informed me that merging locks the table and suggested I use an UPDATE statement instead. </p> <p>From everything I've read, I was under the impression that MERGE INTO and UPDATE have similar incremental locking patterns. Below is an example of the sort of MERGE INTO statement that our application is using.</p> <pre><code>MERGE INTO sample_merge_table smt USING ( SELECT smt.*, sjt.* FROM sample_merge_table smt JOIN some_join_table sjt ON smt.index_value = sjt.secondary_index_value WHERE smt.partition_index = partitionIndex ) umt ON (smt.partition_index = partitionIndex AND smt.index_value = umt.index_value) WHEN MATCHED THEN UPDATE SET... WHEN NOT MATCHED THEN INSERT VALUES... </code></pre> <p>Upon running this statement, what would the locking procedure actually be? Would each table involved in the USING select be locked? Would the sample_merge_table be completely locked, or only the partition that is being accessed? Would the UPDATE statement lock incrementally, or does the MERGE INTO itself already own the required locks?</p>
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