On 06/14/2011 11:04 AM, Robert Haas wrote:
Even if the data were accurate and did not cause plan stability, we have no evidence that using it will improve real-world performance.
That's the dependency Cédric has provided us a way to finally make progress on. Everyone says there's no evidence that this whole approach will improve performance. But we can't collect such data, to prove or disprove it helps, without a proof of concept patch that implements *something*. You may not like the particular way the data is collected here, but it's a working implementation that may be useful for some people. I'll take "data collected at ANALYZE time" as a completely reasonable way to populate the new structures with realistic enough test data to use initially.
Surely at least one other way to populate the statistics, and possibly multiple other ways that the user selects, will be needed eventually. I commented a while ago on this thread: every one of these discussions always gets dragged into the details of how the cache statistics data will be collected and rejects whatever is suggested as not good enough. Until that stops, no progress will ever get made on the higher level details. By its nature, developing toward integrating cached percentages is going to lurch forward on both "collecting the cache data" and "using the cache knowledge in queries" fronts almost independently. This is not a commit candidate; it's the first useful proof of concept step for something we keep talking about but never really doing.
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