(Backport to 5.3)
(variant #2, with fixed coding style)
- Make Mrr_ordered_index_reader::resume_read() restore index position
only if it was saved before with Mrr_ordered_index_reader::interrupt_read().
- The crash was caused because the optimizer called handler->multi_range_read_info()
on a derived temporary table. That table has been created, but not opened yet.
Because of that, handler::table was NULL, which caused crash.
Fixed by changing DS-MRR methods to use handler::table_share instead.
handler::table_share is set in handler ctor, so this should be safe.
- "Using MRR" is no longer shown with range access.
- Instead, both range and BKA accesses will show one of the following:
= "Rowid-ordered scan"
= "Key-ordered scan"
= "Key-ordered Rowid-ordered scan"
depending on whether DS-MRR implementation will do scan keys in order, rowids in order,
or both.
- The patch also introduces a way for other storage engines/MRR implementations to
pass information to EXPLAIN output about the properties of employed MRR scans.
- The problem was that Mrr_ordered_index_reader's interrupt_read() and resume_read() would
save and restore 1) index tuple 2) the rowid (as bytes returned by handler->position()). Clustered
primary key columns were not saved/restored.
They are not explicitly present in the index tuple (i.e. table->key_info[secondary_key].key_parts
doesn't list them), but they are actually there, in particular
table->field[clustered_primary_key_member].part_of_key(secondary_key) == 1. Index condition pushdown
code [correctly] uses the latter as inidication that pushed index condition can refer to clustered PK
members.
The fix was to make interrupt_read()/resume_read() to save/restore clustered primary key members as well,
so that we get correct values for them when evaluating pushed index condition.
[3rd attempt: remove the debugging aids, fix comments in testcase]
Switch from "Disable identical key handling optimization when
IndexConditionPushdown is used" approach
To
an approach where we save/restore index tuple and so can use index condition pushdown.
- Make Mrr_ordered_index_reader() save the rowid across scan interruptions
Also
- Fix compiler warning for setup_buffer_sizes()
- Add commented key_copy/key_restore for better handling of a similar issue
with index record being destroyed by scan interruption (which causes
incorrect evaluation of pushed index condition later on).
