ENH: improve performance of read_dataframe if a filter is used #577
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In
read_dataframewithout arrow, the number of rows of the result was counted first, and then the full data was read.Especially when using a filter, counting the rows can take significant time. If the filter limits the rows a lot counting the rows can even take the same time as the subsequent reading of all data.
This PR removes the rowcount before reading to improve performance.