On Thu, May 11, 2023 at 1:56 AM Peter J. Holzer <hjp-pgsql@hjp.at> wrote:
On 2023-05-10 22:52:47 +0200, Marc Millas wrote: > On Wed, May 10, 2023 at 7:24 PM Peter J. Holzer <hjp-pgsql@hjp.at> wrote: > > On 2023-05-10 16:35:04 +0200, Marc Millas wrote: > > Unique (cost=72377463163.02..201012533981.80 rows=1021522829864 width= > 97) > > -> Gather Merge (cost=72377463163.02..195904919832.48 rows= > 1021522829864 width=97) > ... > > -> Parallel Hash Left Join (cost= > 604502.76..1276224253.51 rows=204304565973 width=97) > > Hash Cond: ((t1.col_ano)::text = (t2.col_ano)::text) > ... > > > > //so.. the planner guess that those 2 join will generate 1000 billions > rows... > > Are some of the col_ano values very frequent? If say the value 42 occurs > 1 million times in both table_a and table_b, the join will create 1 > trillion rows for that value alone. That doesn't explain the crash or the > disk usage, but it would explain the crazy cost (and would probably be a > hint that this query is unlikely to finish in any reasonable time). > > > good guess, even if a bit surprising: there is one (and only one) "value" which > fit your supposition: NULL
But NULL doesn't equal NULL, so that would result in only one row in the left join. So that's not it.
if so... how ???
hp
-- _ | Peter J. Holzer | Story must make more sense than reality. |_|_) | | | | | hjp@hjp.at | -- Charles Stross, "Creative writing __/ | http://www.hjp.at/ | challenge!"