Bind Variables, almost right.

Sometimes I get a bit sarcastic with and about developers, this is unfair as for the most part the ones I have worked closely have either been very good oracle developers or very good c++/java/VB6/whatever developers with a real interest in doing things the right way and have been receptive to constructive (but grumpy feedback).

This gem in a vendors application however brought out the sarcasm.

  column_1 = :1, column2 = :2, ..............
  column_125 = :125, column_126 = :126
   column_127 = 'GotBoredWithBindVariablesDidWe?';

I can’t work the logic out here, the code is already written to use bind variables it took extra code to stick a literal in there, as the application is written in c using the oci libraries these guys are supposed to be rocket surgeons. There isn’t even a justification based on skewed data column_127 is the primary key so every update updates one row and there is only one plan ever used. Added to that the design of the process is such that the application caches updates then send in 400 at a time , committing after each update just to make sure performance really suffers except for end of day processing where all 27,000 rows are updated at least there is only a single commit during that specific piece.

So far so bad, however the worst impact we see is because we are using Automatic Memory management the shared pool grows larger over time as it tries to cache all the execution plans. After three weeks we get to the point of other processes suffering form either not enough buffers or increases in mutex and library cache latch waits, the solution? restart the database every two weeks and the spfile to reset the values of __db_cache_size and __shared_pool_size. Yes we could use manual memory management but the vendors application compute guide specifies AMM changing to manual memory management is still being assessed by their performance team.

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