On Sat, Jun 18, 2016 at 5:14 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > . In 9.x, that's broken and it falls back to > get_typavgwidth's default guess of 32 bytes. If what you've actually > got is, say, varchar(255) and most of the entries actually approach > that length, this could result in a drastic underestimate, possibly > leading to OOM from hash table growth.
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This seems more likely to result in the converse. 32 bytes is enough distinct values I imagine it's going to avoid a hash join. (and In any case if you have a varchar(n) where n>32 then it's probably a bad bet to assume n gives much information about the typical length of the strings). On the other hand if what you've actually got is a varchar(1) or something like that then indeed a hash join might have been a good choice. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
