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The variable controls the amount of sampling analyze table performs. If ANALYZE table with histogram collection is too slow, one can reduce the time taken by setting analyze_sample_percentage to a lower value of the total number of rows. Setting it to 0 will use a formula to compute how many rows to sample: The number of rows collected is capped to a minimum of 50000 and increases logarithmically with a coffecient of 4096. The coffecient is chosen so that we expect an error of less than 3% in our estimations according to the paper: "Random Sampling for Histogram Construction: How much is enough?” – Surajit Chaudhuri, Rajeev Motwani, Vivek Narasayya, ACM SIGMOD, 1998. The drawback of sampling is that avg_frequency number is computed imprecisely and will yeild a smaller number than the real one.