On 2015-07-20 12:18, Petr Jelinek wrote:
On 2015-07-19 22:56, Tom Lane wrote:
* You might have expected me to move the tsmseqscan and tsmpagemode flags
into the TsmRoutine struct, but instead this API puts equivalent flags
into the SampleScanState struct. The reason for that is that it lets
the settings be determined at runtime after inspecting the TABLESAMPLE
parameters, which I think would be useful. For example, whether to use
the bulkread strategy should probably depend on what the sampling
percentage is.
I think this ignores one aspect of the old API. That is, we allowed the
sampling method to specify which kind of input parameters it accepts.
This is why for example the tsm_system_rows accepts integer while system
and bernoulli both accept float8. This part of the API is certainly not
needed for bernoulli and system sampling but if we ever want to do
something more sophisticated like stratified sampling which Simon
mentioned several times, specifying just percentages is not going to be
enough.
Actually I see the tsmapi has support for this, so please ignore the noise.
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Petr Jelinek http://www.2ndQuadrant.com/
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