Hi, Attached is a patch implementing a new aggregate function md5_agg() to compute the aggregate MD5 sum across a number of rows. This is something I've wished for a number of times. I think the primary use case is to do a quick check that 2 tables, possibly on different servers, contain the same data, using a query like
SELECT md5_agg(foo.*::text) FROM (SELECT * FROM foo ORDER BY id) foo; or SELECT md5_agg(foo.*::text ORDER BY id) FROM foo; these would be equivalent to SELECT md5(string_agg(foo.*::text, '' ORDER BY id)) FROM foo; but without the excessive memory consumption for the intermediate concatenated string, and the resulting 1GB table size limit. I've added 2 variants: md5_agg(text) and md5_agg(bytea) to match the 2 variants of md5(), so pure binary data can also be checksummed. In passing, I've tidied up and optimised the code in md5.c a bit --- specifically I've removed the malloc()/memcpy()/free() code that was unnecessarily making a copy of the entire input data just to pad it and append the bit count. This reduces the memory consumption of the existing md5() functions for large inputs, and gives a modest performance boost. As a result, the md5() function can no longer throw an out-of-memory error. Regards, Dean
md5_agg.patch
Description: Binary data
-- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
