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The following pattern is quite common in database
IF EXISTS(some query) BEGIN
When such code runs in high concurrency situations, it may
not work as expected. I will provide a repro when such logic fails 40% of the
time. The following script provides a test table and attempts to ...
If your data has a small percentage of duplicates, then IGNORE_DUP_KEY
may speed up your inserts. For larger amounts of duplicates, IGNORE_DUP_KEY may
slow them down significantly. I set up two tables, stripping down all the
irrelevant details, as follows:
CREATE TABLE t1(n INT NOT NULL PRIMARY KEY)
CREATE TABLE ...