On 01/23/2015 10:42 PM, Ravi Kiran wrote:
hi, I want to know what kind of hash function postgresql uses while joining. I was debugging through gdb, I found out that it is not using bob jenkins hash function but a different hash function *hash_uint32() and hash_any() *functions if the joining attribute is an integer, and a different kind of hash function for a different type of joining attribute. I want to know whether the hash functions will change if the number of tuples in the table are very large or very low, and if it changes, please tell me what hash function it uses if the tuples are very large and what hash function it uses if the number is very low, also I came to know that the hash function will change depending on the type of the attribute on which the join takes place, but will it always remains the same for the integer type of joining attribute or will it it change.
Seems a good starting point is here: http://git.postgresql.org/gitweb/?p=postgresql.git;a=tree;f=src/backend/access/hash;h=6e44d337d3dc3e8d5439e2dbbc54ce0c33d3b5d4;hb=8ca336f4ac3f08a5f23e76c6e9a5f2c8064f5883 In particular, hashfunc.c
thanks
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