How does postgres calculate multi column hashes?

Question

In PG I have a table which is using partition by hash (*text*, *bigint*) looking at a previous answer the functions used for hashing can be seen however I'm unsure which function is used to build combined hashes?

Is it treating the partition keys as a record and using hash_record?

Ultimately I want to know this to rebuild the hashing function in Java to optimise reads and writes to specific partitions.

score 1 · Accepted Answer · answered Nov 07 '22 at 14:10

1

The hash_combine64 is used for calculating the ultimate hash value. According to the comments in the code it's based on the boost's hash_combine approach. Also, you can find the whole partition calculation algorithm in compute_partition_hash_value function.

answered Nov 07 '22 at 14:10

Ilia Maskov

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is there a reason I cant see the combine function when I run `\df hash_combine64` (using PG 14.5) – Stephen Flavin Nov 07 '22 at 15:48
No idea why it's not propagated there. Historical reasons? – Ilia Maskov Nov 08 '22 at 15:00

How does postgres calculate multi column hashes?

1 Answers1