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Commitcc988fb

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Improve ResourceOwners' behavior for large numbers of owned objects.
The original coding was quite fast so long as objects were alwaysreleased in reverse order of addition; otherwise, it degenerated intoO(N^2) behavior due to searching for the array element to delete.Improve matters by switching to hashed storage when the number ofobjects of a given type exceeds 64. (The cutover point is open todiscussion, of course, but some simple performance testing suggeststhat hashing has enough overhead to be a loser below there.)Also, refactor resowner.c so that we don't need N copies of the arraymanagement code. Since all the resource IDs the code currently needsto deal with are either pointers or integers, it seems sufficient tocreate a one-size-fits-all infrastructure in which everything isconverted to a Datum for storage.Aleksander Alekseev, reviewed by Stas Kelvich, further fixes by me
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‎src/backend/access/hash/hashfunc.c

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@@ -297,6 +297,9 @@ hashvarlena(PG_FUNCTION_ARGS)
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* of 2. There is no need to do mod a prime (mod is sooo slow!).
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* If you need less than 32 bits, use a bitmask.
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*
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* This procedure must never throw elog(ERROR); the ResourceOwner code
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* relies on this not to fail.
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*
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* Note: we could easily change this function to return a 64-bit hash value
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* by using the final values of both b and c. b is perhaps a little less
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* well mixed than c, however.

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