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d9d0e78039
This solves the current problem in the optimizer - SELECT FROM big_table - SELECT from small_table where small_table.eq_ref_key=big_table.id The old code assumed that each eq_ref access will cause an IO. As the cost of IO is high, this dominated the cost for the later table which caused the optimizer to prefer table scans + join cache over index reads. This patch fixes this issue by limit the number of expected IO calls, for rows and index separately, to the size of the table or index or the number of accesses that we except in a range for the index. The major changes are: - Adding a new structure ALL_READ_COST that is mainly used in best_access_path() to hold the costs parts of the cost we are calculating. This allows us to limit the number of IO when multiplying the cost with the previous row combinations. - All storage engine cost functions are changed to return IO_AND_CPU_COST. The virtual cost functions should now return in IO_AND_CPU_COST.io the number of disk blocks that will be accessed instead of the cost of the access. - We are not limiting the io_blocks for table or index scans as we assume that engines may not store these in the 'hot' part of the cache. Table and index scan also uses much less IO blocks than key accesses, so the original issue is not as critical with scans. Other things: OPT_RANGE now holds a 'Cost_estimate cost' instead a lot of different costs. All the old costs, like index_only_read, can be extracted from 'cost'. - Added to the start of some functions 'handler *file= table->file' to shorten the code that is using the handler. - handler->cost() is used to change a ALL_READ_COST or IO_AND_CPU_COST to 'cost in milliseconds' - New functions: handler::index_blocks() and handler::row_blocks() which are used to limit the IO. - Added index_cost and row_cost to Cost_estimate and removed all not needed members. - Removed cost coefficients from Cost_estimate as these don't make sense when costs (except IO_BLOCKS) are in milliseconds. - Removed handler::avg_io_cost() and replaced it with DISK_READ_COST. - Renamed best_range_rowid_filter_for_partial_join() to best_range_rowid_filter() as using the old name made rows too long. - Changed all SJ_MATERIALIZATION_INFO 'Cost_estimate' variables to 'double' as Cost_estimate power was not used for these and thus just caused storage and performance overhead. - Changed cost_for_index_read() to use 'worst_seeks' to only limit IO, not number of table accesses. With this patch worst_seeks is probably not needed anymore, but I kept it around just in case. - Applying cost for filter got to be much shorter and easier thanks to the API changes. - Adjusted cost for fulltext keys in collaboration with Sergei Golubchik. - Most test changes caused by this patch is that table scans are changed to use indexes. - Added ha_seq::keyread_time() and ha_seq::key_scan_time() to get make checking number of potential IO blocks easier during debugging. |
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| .. | ||
| CMakeLists.txt | ||
| ha_tina.cc | ||
| ha_tina.h | ||
| transparent_file.cc | ||
| transparent_file.h | ||