| From: | Sailesh Krishnamurthy <sailesh(at)cs(dot)berkeley(dot)edu> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Group-count estimation statistics |
| Date: | 2005-01-28 23:42:09 |
| Message-ID: | mjqwttxnmsu.fsf@drones.CS.Berkeley.EDU |
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| Lists: | pgsql-hackers |
>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
Tom> The only real solution, of course, is to acquire cross-column
Tom> statistics, but I don't see that happening in the near
Tom> future.
Another approach is a hybrid hashing scheme where we use a hash table
until we run out of memory at which time we start spilling to disk. In
other words, no longer use SortAgg at all ..
Under what circumstances will a SortAgg consumer more IOs than a
hybrid hash strategy ?
--
Pip-pip
Sailesh
http://www.cs.berkeley.edu/~sailesh
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