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2b1f0b8757
fixed several defects in the greedy optimization: 1) The greedy optimizer calculated the 'compare-cost' (CPU-cost) for iterating over the partial plan result at each level in the query plan as 'record_count / (double) TIME_FOR_COMPARE' This cost was only used locally for 'best' calculation at each level, and *not* accumulated into the total cost for the query plan. This fix added the 'CPU-cost' of processing 'current_record_count' records at each level to 'current_read_time' *before* it is used as 'accumulated cost' argument to recursive best_extension_by_limited_search() calls. This ensured that the cost of a huge join-fanout early in the QEP was correctly reflected in the cost of the final QEP. To get identical cost for a 'best' optimized query and a straight_join with the same join order, the same change was also applied to optimize_straight_join() and get_partial_join_cost() 2) Furthermore to get equal cost for 'best' optimized query and a straight_join the new code substrcated the same '0.001' in optimize_straight_join() as it had been already done in best_extension_by_limited_search() 3) When best_extension_by_limited_search() aggregated the 'best' plan a plan was 'best' by the check : 'if ((search_depth == 1) || (current_read_time < join->best_read))' The term '(search_depth == 1' incorrectly caused a new best plan to be collected whenever the specified 'search_depth' was reached - even if this partial query plan was more expensive than what we had already found. |
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