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e99f2b1c4e
that implement add_index The problem was that ALTER TABLE blocked reads on an InnoDB table while adding a secondary index, even if this was not needed. It is only needed for the final step where the .frm file is updated. The reason queries were blocked, was that ALTER TABLE upgraded the metadata lock from MDL_SHARED_NO_WRITE (which blocks writes) to MDL_EXCLUSIVE (which blocks all accesses) before index creation. The way the server handles index creation, is that storage engines publish their capabilities to the server and the server determines which of the following three ways this can be handled: 1) build a new version of the table; 2) change the existing table but with exclusive metadata lock; 3) change the existing table but without metadata lock upgrade. For InnoDB and secondary index creation, option 3) should have been selected. However this failed for two reasons. First, InnoDB did not publish this capability properly. Second, the ALTER TABLE code failed to made proper use of the information supplied by the storage engine. A variable need_lock_for_indexes was set accordingly, but was not later used. This patch fixes this problem by only doing metadata lock upgrade before index creation/deletion if this variable has been set. This patch also changes some of the related terminology used in the code. Specifically the use of "fast" and "online" with respect to ALTER TABLE. "Fast" was used to indicate that an ALTER TABLE operation could be done without involving a temporary table. "Fast" has been renamed "in-place" to more accurately describe the behavior. "Online" meant that the operation could be done without taking a table lock. However, in the current implementation writes are always prohibited during ALTER TABLE and an exclusive metadata lock is held while updating the .frm, so ALTER TABLE is not completely online. This patch replaces "online" with "in-place", with additional comments indicating if concurrent reads are allowed during index creation/deletion or not. An important part of this update of terminology is renaming of the handler flags used by handlers to indicate if index creation/deletion can be done in-place and if concurrent reads are allowed. For example, the HA_ONLINE_ADD_INDEX_NO_WRITES flag has been renamed to HA_INPLACE_ADD_INDEX_NO_READ_WRITE, while HA_ONLINE_ADD_INDEX is now HA_INPLACE_ADD_INDEX_NO_WRITE. Note that this is a rename to clarify current behavior, the flag values have not changed and no flags have been removed or added. Test case added to innodb_mysql_sync.test. |
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