A second DML in a transaction for a table of non-rollbackable engine
leads to a cache corruption, because the cache wasn't reset after a
statement end, but also wasn't destroyed.
This patch resets the cache for a reuse by subsequent statements in
current transaction.
In case of a non-recovery XA rollback/commit in the same connection,
thon->rollback is called instead of rollback_by_xid, Though previously,
thd_ha_data was moved to thd->transaction->xid_state.xid in hton->prepare.
Like it wasn't enough, XA PREPARE can be skipped upon user and thus we
can end up in hton->commit/rollback with and unprepared XA, so checking
xid_state.is_explicit_XA is not enough -- we should check
xid_state.get_state_code() == XA_PREPARED, which will also guarantee
is_explicit_XA() == true.
XA support for online alter was totally missing.
Tying on binlog_hton made this hardly visible: simply having binlog_commit
called from xa_commit made an impression that it will automagically work
for online alter, which turns out wrong: all binlog does is writes
"XA END" into trx cache and flushes it to a real binlog.
In comparison, online alter can't do the same, since online replication
happens in a single transaction.
Solution: make a dedicated XA support.
* Extend struct xid_t with a pointer to Online_alter_cache_list
* On prepare: move online alter cache from THD::ha_data to XID passed
* On XA commit/rollback: use the online alter cache stored in this XID.
This makes us pass xid_cache_element->xid to xa_commit/xa_rollback
instead of lex->xid
* Use manual memory management for online alter cache list, instead of
mem_root allocation, since we don't have mem_root connected to the XA
transaction.
Use standard handlerton functions for savepoint add/rollback.
To identify the savepoint, the pointer passed is used.
Every table that has online alter in progress maintains a list of
savepoints independently.
Also this removes setting a value to a global variable savepoint_alloc_size
without any protection, which was a race condition bug.
Move all the functions dedicated to online alter to a newly created
online_alter.cc.
With that, make many functions static and simplify the static functions
naming.
Also, rename binlog_log_row_online_alter -> online_alter_log_row.
