During several profile runs I've seen the division in
        if (action == HASH_ENTER || action == HASH_ENTER_NULL)
                 * Can't split if running in partitioned mode, nor if frozen, 
nor if
                 * table is the subject of any active hash_seq_search scans.  
                 * order of these tests is to try to check cheaper conditions 
                if (!IS_PARTITIONED(hctl) && !hashp->frozen &&
                        hctl->freeList[0].nentries / (long) (hctl->max_bucket + 
1) >= hctl->ffactor &&
                        (void) expand_table(hashp);
taking up significant amounts of time.  Which is not particularly
surprising: A signed 64 integer division (which is what we're dealing
with here) takes up to ~100 cycles, is microcoded, and prevents
instruction level parallelism.

We could cast to unsigned long - which would be faster - but it seems
like it'd be better to compute a threshold in
init_htab()/expand_table(), and make that && hctl->freeList[0].nentries >= 
or somesuch.

I don't plan to do that, but I wanted to document it, should somebody
else be motivated to look into this.


Andres Freund

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