- QUICK_INDEX_MERGE_SELECT deinitializes its rnd_pos() scan when it reaches EOF, but we
need to make the deinitialization in QUICK_INDEX_MERGE_SELECT destructor also. This is because
certain execution strategies can stop scanning without reaching EOF, then then try to do a full
table scan on this table. Failure to deinitialize caused the full scan to use (already empty)
table->sort and produce zero records.
When analyzing the possible index use cases the server was re-using an internal structure.
This is wrong, as this internal structure gets updated during the analysis.
Fixed by making a copy of the internal structure for every place it needs to be used.
Also stopped the generation of empty SEL_TREE structures that unnecessary
complicate the analysis.
Only MyISAM tables locked with LOCK TABLES ... WRITE were affected.
A query that is optimized with index_merge doesn't reflect rows
inserted within LOCK TABLES.
MyISAM doesn't flush a state within LOCK TABLES. index_merge
optimization creates a copy of the handler, which thus gets
outdated MyISAM state.
New handler->clone() method is introduced to fix this problem.
For non-MyISAM storage engines it allocates a handler and opens
it with ha_open(). For MyISAM it additionally copies MyISAM state
pointer to cloned handler.
1. Fix index access costs for MERGE tables, set block_size=myisam_block_size/#underlying_tables
instead of 0 which it was before.
2. Make index scans on MERGE table to return records in (key_tuple, merge_table_rowid) order,
instead of just (key_tuple) order. This makes an index scan on MERGE table to be truly a ROR-scan
which is a requirement for index_merge union/intersection.
myisam_max_extra_sort_file_size is depricated
Ensure that myisam_data_pointer_size is honoured when creating new MyISAM files
Changed default value of myisam_data_pointer_size from 4 to 6 to get rid of 'table-is-full' errors
