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Subject: Re: Support loser tree for k-way merge
Date: Thu, 4 Dec 2025 11:49:07 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAA5RZ0u=WDa-v+8Y_yE4WeRS8VtmcmQGuWVjZFCqZcXx-hEP3w@mail.gmail.com>
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Hi,
Thank you for your reply.
> Can we drive the decision for what to do based on optimizer
> stats, i.e. n_distinct and row counts? Not sure what the calculation would
> be specifically, but something else to consider.
>
> We can still provide the GUC to override the optimizer decisions,
> but at least the optimizer, given up-to-date stats, may get it right most
> of the time.
That makes sense to me.
TODO
====
1) Consider optimizer statistics when deciding whether to use the heap or the loser tree.
2) Do we need a USEMEM() call to the array of losers?
3) Now the array length of losers is MAXORDER * 2, and in fact MAXORDER is enough, need some refactor of the code. (Is it worth doing?)
4) Add more code comments and doc.
Help are welcome!
--
Regards,
ChangAo Chen
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