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I am creating my own index method in PostgreSQL based on GiST as extension. I want one of my functions (check out Examples section) in my operator to behave differently based on a value defined by the user- I want to avoid the user having to drop and create operators again.

So, I was looking at introducing a GUC variable. However, I am not so sure how to implement this appropriately. Right now in my implementation, the operator is being created with the value of GUC and is not behaving differently once GUC value changes at runtime.

I am not sure if I have to somehow change the signature of the function to use GUC or if I must introduce some pointer to the GUC. I cannot find any helpful material and I do not fully understand the internals to achieve this goal.

What best practices must I use for introducing an operator which changes behaviour at runtime? Unfortunately, I cannot find much information on writing internal functions/ operators/GUC in this context and so it would be great to hear any kind of feedback at all.

Zeruno
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1 Answers1

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A “GUC” (Grand Unified Configuration) is simply a global C variable in your program code, so changing its value will take effect as soon as your code reads the variable.

Your function will be in a shared object that is loaded into PostgreSQL, and you can use the _PG_init() function that is called at load time to register a new GUC with the DefineCustomXXXVariable() functions.

Your GUC can then be set like any other GUC.

I recommend that you look at contrib modules like auto_explain to see how they do it.

Laurenz Albe
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