Re: Bug? ExecChooseHashTableSize() got assertion failed with crazy number of rows

> -----Original Message-----
> From: David Rowley [mailto:david.rowley@2ndquadrant.com]
> Sent: Wednesday, August 19, 2015 9:00 AM
> The size of your hash table is 101017630802 bytes, which is:
>
> david=# select pg_size_pretty(101017630802);
>
>  pg_size_pretty
> ----------------
>  94 GB
> (1 row)
>
> david=# set work_mem = '94GB';
> ERROR:  98566144 is outside the valid range for parameter "work_mem" (64 ..
> 2097151)
>

Hmm. Why I could set work_mem = '96GB' without error.

It was described in the postgresql.conf.

  postgres=# SHOW work_mem;
   work_mem
  ----------
   96GB
  (1 row)

> So I think the only way the following could cause an error, is if bucket_size
> was 1, which it can't be.
>
> lbuckets = 1 << my_log2(hash_table_bytes / bucket_size);
>
>
> I think one day soon we'll need to allow larger work_mem sizes, but I think there's
> lots more to do than this change.
>
I oversight this limitation, but why I can bypass GUC limitation check?