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4 commits
| Author | SHA1 | Message | Date | |
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Monty
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3c1b7fb03e |
Adjust costs for rowid filter
- Use log2() insted of log() - Added missing ''+' when calculating rowid setup cost - Adjusted ROWID_FILTER_PER_ELEMENT_MODIFIER (from 3 to 1) Other things: - Adjusted cost for index_merge where rows_out < 1.0 The effects of the changes: - rowid filter will have higher setup cost - rowid filter will have slightly less costs per row This can be seen in mtr where some tests, with 'small tables or that uses rowid filters with many rows, will not use rowid filter anymore. |
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Monty
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66dde8a54e |
Added rowid_filter support to Aria
This includes: - cleanup and optimization of filtering and pushdown engine code. - Adjusted costs for rowid filters (based on extensive testing and profiling). This made a small two changes to the handler_rowid_filter_is_active() API: - One should not call it with a zero pointer! - One does not need to call handler_rowid_filter_is_active() for every row anymore. It is enough to check if filter is active by calling it call it during index_init() or when handler::rowid_filter_changed() is called The changes was to avoid unnecessary function calls and checks if pushdown conditions and rowid_filter is not used. Updated costs for rowid_filter_lookup() to be closer to reality. The old cost was based only on rowid_compare_cost. This is now changed to take into account the overhead in checking the rowid. Changed the Range_rowid_filter class to use DYNAMIC_ARRAY directly instead of Dynamic_array<>. This was done to be able to use the new append_dynamic() functions which gives a notable speed improvment compared to the old code. Removing the abstraction also makes the code easier to understand. The cost of filtering is now slightly lower than before, which is reflected in some test cases that is now using rowid filters. |
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Monty
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d9d0e78039 |
Add limits for how many IO operations a table access will do
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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Monty
|
b66cdbd1ea |
Changing all cost calculation to be given in milliseconds
This makes it easier to compare different costs and also allows
the optimizer to optimizer different storage engines more reliably.
- Added tests/check_costs.pl, a tool to verify optimizer cost calculations.
- Most engine costs has been found with this program. All steps to
calculate the new costs are documented in Docs/optimizer_costs.txt
- User optimizer_cost variables are given in microseconds (as individual
costs can be very small). Internally they are stored in ms.
- Changed DISK_READ_COST (was DISK_SEEK_BASE_COST) from a hard disk cost
(9 ms) to common SSD cost (400MB/sec).
- Removed cost calculations for hard disks (rotation etc).
- Changed the following handler functions to return IO_AND_CPU_COST.
This makes it easy to apply different cost modifiers in ha_..time()
functions for io and cpu costs.
- scan_time()
- rnd_pos_time() & rnd_pos_call_time()
- keyread_time()
- Enhanched keyread_time() to calculate the full cost of reading of a set
of keys with a given number of ranges and optional number of blocks that
need to be accessed.
- Removed read_time() as keyread_time() + rnd_pos_time() can do the same
thing and more.
- Tuned cost for: heap, myisam, Aria, InnoDB, archive and MyRocks.
Used heap table costs for json_table. The rest are using default engine
costs.
- Added the following new optimizer variables:
- optimizer_disk_read_ratio
- optimizer_disk_read_cost
- optimizer_key_lookup_cost
- optimizer_row_lookup_cost
- optimizer_row_next_find_cost
- optimizer_scan_cost
- Moved all engine specific cost to OPTIMIZER_COSTS structure.
- Changed costs to use 'records_out' instead of 'records_read' when
recalculating costs.
- Split optimizer_costs.h to optimizer_costs.h and optimizer_defaults.h.
This allows one to change costs without having to compile a lot of
files.
- Updated costs for filter lookup.
- Use a better cost estimate in best_extension_by_limited_search()
for the sorting cost.
- Fixed previous issues with 'filtered' explain column as we are now
using 'records_out' (min rows seen for table) to calculate filtering.
This greatly simplifies the filtering code in
JOIN_TAB::save_explain_data().
This change caused a lot of queries to be optimized differently than
before, which exposed different issues in the optimizer that needs to
be fixed. These fixes are in the following commits. To not have to
change the same test case over and over again, the changes in the test
cases are done in a single commit after all the critical change sets
are done.
InnoDB changes:
- Updated InnoDB to not divide big range cost with 2.
- Added cost for InnoDB (innobase_update_optimizer_costs()).
- Don't mark clustered primary key with HA_KEYREAD_ONLY. This will
prevent that the optimizer is trying to use index-only scans on
the clustered key.
- Disabled ha_innobase::scan_time() and ha_innobase::read_time() and
ha_innobase::rnd_pos_time() as the default engine cost functions now
works good for InnoDB.
Other things:
- Added --show-query-costs (\Q) option to mysql.cc to show the query
cost after each query (good when working with query costs).
- Extended my_getopt with GET_ADJUSTED_VALUE which allows one to adjust
the value that user is given. This is used to change cost from
microseconds (user input) to milliseconds (what the server is
internally using).
- Added include/my_tracker.h ; Useful include file to quickly test
costs of a function.
- Use handler::set_table() in all places instead of 'table= arg'.
- Added SHOW_OPTIMIZER_COSTS to sys variables. These are input and
shown in microseconds for the user but stored as milliseconds.
This is to make the numbers easier to read for the user (less
pre-zeros). Implemented in 'Sys_var_optimizer_cost' class.
- In test_quick_select() do not use index scans if 'no_keyread' is set
for the table. This is what we do in other places of the server.
- Added THD parameter to Unique::get_use_cost() and
check_index_intersect_extension() and similar functions to be able
to provide costs to called functions.
- Changed 'records' to 'rows' in optimizer_trace.
- Write more information to optimizer_trace.
- Added INDEX_BLOCK_FILL_FACTOR_MUL (4) and INDEX_BLOCK_FILL_FACTOR_DIV (3)
to calculate usage space of keys in b-trees. (Before we used numeric
constants).
- Removed code that assumed that b-trees has similar costs as binary
trees. Replaced with engine calls that returns the cost.
- Added Bitmap::find_first_bit()
- Added timings to join_cache for ANALYZE table (patch by Sergei Petrunia).
- Added records_init and records_after_filter to POSITION to remember
more of what best_access_patch() calculates.
- table_after_join_selectivity() changed to recalculate 'records_out'
based on the new fields from best_access_patch()
Bug fixes:
- Some queries did not update last_query_cost (was 0). Fixed by moving
setting thd->...last_query_cost in JOIN::optimize().
- Write '0' as number of rows for const tables with a matching row.
Some internals:
- Engine cost are stored in OPTIMIZER_COSTS structure. When a
handlerton is created, we also created a new cost variable for the
handlerton. We also create a new variable if the user changes a
optimizer cost for a not yet loaded handlerton either with command
line arguments or with SET
@@global.engine.optimizer_cost_variable=xx.
- There are 3 global OPTIMIZER_COSTS variables:
default_optimizer_costs The default costs + changes from the
command line without an engine specifier.
heap_optimizer_costs Heap table costs, used for temporary tables
tmp_table_optimizer_costs The cost for the default on disk internal
temporary table (MyISAM or Aria)
- The engine cost for a table is stored in table_share. To speed up
accesses the handler has a pointer to this. The cost is copied
to the table on first access. If one wants to change the cost one
must first update the global engine cost and then do a FLUSH TABLES.
This was done to be able to access the costs for an open table
without any locks.
- When a handlerton is created, the cost are updated the following way:
See sql/keycaches.cc for details:
- Use 'default_optimizer_costs' as a base
- Call hton->update_optimizer_costs() to override with the engines
default costs.
- Override the costs that the user has specified for the engine.
- One handler open, copy the engine cost from handlerton to TABLE_SHARE.
- Call handler::update_optimizer_costs() to allow the engine to update
cost for this particular table.
- There are two costs stored in THD. These are copied to the handler
when the table is used in a query:
- optimizer_where_cost
- optimizer_scan_setup_cost
- Simply code in best_access_path() by storing all cost result in a
structure. (Idea/Suggestion by Igor)
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