Hello,
In the scope of the fix for Bug#42230 "during add index, cannot do
queries on storage engines that implement add_index" we are renaming
some of the flags defined in handler.h to better reflect their current
behavior. This change will affect MySQL version 5.5+ (not 5.1).
The purpose of this e-mail is to explain the changes to any external
storage engine developers that might be affected, and also ask if anyone
wants us to keep backward compatible defines.
In the patch, we're changing some of the terminology used in the server
code related to ALTER TABLE - namely "online" and "fast". According to
comments in handler.h, "online" means "without a table lock" However,
the 5.5 ALTER TABLE implementation currently always blocks writes and
requires exclusive table access for the final step(s). The term "online"
therefore seems misleading.
"fast ALTER TABLE" is described as "off-line without re-create of the
table (but with a table lock)". In other words, not using a temporary
table. Our objection here is that "fast" isn't very descriptive. Another
problem is that "fast" and "online" seem to be used somewhat
interchangeably throughout the code.
We have replaced "fast alter table" by "in-place alter table" to
indicate alter table done without a temporary table. The term was
inspired by http://en.wikipedia.org/wiki/In-place_algorithm
Generally, "online" was also replaced by "in-place". The only practical
difference between "online" and "fast" was that "online" allowed for
concurrent reads and this was seldom relevant in the context "online"
was used.
This has consequences for flags defined in handler.h. These flags are:
HA_ONLINE_ADD_INDEX_NO_WRITES
HA_ONLINE_DROP_INDEX_NO_WRITES
HA_ONLINE_ADD_UNIQUE_INDEX_NO_WRITES
HA_ONLINE_DROP_UNIQUE_INDEX_NO_WRITES
HA_ONLINE_ADD_PK_INDEX_NO_WRITES
HA_ONLINE_DROP_PK_INDEX_NO_WRITES
and
HA_ONLINE_ADD_INDEX
HA_ONLINE_DROP_INDEX
HA_ONLINE_ADD_UNIQUE_INDEX
HA_ONLINE_DROP_UNIQUE_INDEX
HA_ONLINE_ADD_PK_INDEX
HA_ONLINE_DROP_PK_INDEX
The first group of flags indicated that a storage engine was capable of
"fast" but not "online" add/drop of indexes. These have been renamed to
HA_INPLACE_ADD_INDEX_NO_READ_WRITE (etc.)
The second group of flags were used for "fast" and "online" add/drop of
indexes. These have been renamed to HA_INPLACE_ADD_INDEX_NO_WRITE (etc.)
No changes have been made to the meaning of the flags.
--- Jon Olav Hauglid
