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Dear all,
first let me thank the PostgreSQL developers for implementing the incredibly helpful window functions. This is one of the features I use most often.
But, as my requirements are perhaps a bit special, I always want more ;) Now I am trying to implement my own window function using C-Language-Functions and the window function API, which, by the way, gives a very nice interface for developing my own window functions.
My function needs a very long time to execute while the underlying algorithm should be relatively fast.
Currently I access rows of the window partition using the WinGetFuncArgInPartition function. However, what I noticed is that this function seems incredibly slow when the partition looked at is rather large – for my case about 1245000 rows. I call that function about 10 times for each row at the first row of each partition (using more or less a random access schema) and compute some summary statistics. When I just randomly stop the running function with a debugger, it nearly always seems to be caught in BufFileRead(), thus my assumption is that this function and the call to WinGetFuncArgInPartition is the bottleneck of my function.
Is anybody able to explain why I get such bad runtimes? And even better, do you see a way to speed up WinGetFuncArgInPartition or replace it by something more performant? Would linear access be faster?
Thank you for your support. Thilo Schneider
P.S.: I know my question might be better suited the hackers-list. However, as all questions should be asked elsewhere first, let’s have a try :)
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