Horton

Re: BUG #16863: Assert failed in set_plain_rel_size() on processing ~* with a long prefix

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-bugs@lists.postgresql.org
Date: 2021-02-12T21:00:00Z
Lists: pgsql-bugs 
Hello Tom,
12.02.2021 23:37, Tom Lane wrote:
> Alexander Lakhin <exclusion@gmail.com> writes:
>> I've found a division that produces NaN:
>> sel /= pow(FIXED_CHAR_SEL, fixed_prefix_len);
> Hmm.  I'm not getting a NaN AFAICT, but I am getting pretty darn weird
> estimates.  I agree this needs some kind of clamp.
>
> regression=# create table test (t text);
> CREATE TABLE
> regression=# explain SELECT * FROM test WHERE t ~* ('^' || repeat('-', 500));
> ...
>  Seq Scan on test  (cost=0.00..27.00 rows=10000000000000000159028911097599180468360808563945281389781327557747838772170381060813469985856815104 width=32)
The same number I've seen on the master branch. But on REL_13_STABLE I
get a NaN and then the assertion failure. (I've chosen the version 13.2
in the bug report, but it's really delayed somewhere.)
Though that division produced a NaN for me on both branches.

Best regards,
Alexander

Commits

  1. Avoid divide-by-zero in regex_selectivity() with long fixed prefix.

  2. Prevent overly large and NaN row estimates in relations