MDEV-16329 [5/5] ALTER ONLINE TABLE

* Log rows in online_alter_binlog.
* Table online data is replicated within dedicated binlog file
* Cached data is written on commit.
* Versioning is fully supported.
* Works both wit and without binlog enabled.

* For now savepoints setup is forbidden while ONLINE ALTER goes on.
  Extra support is required. We can simply log the SAVEPOINT query events
  and replicate them together with row events. But it's not implemented
  for now.

* Cache flipping:

  We want to care for the possible bottleneck in the online alter binlog
  reading/writing in advance.

  IO_CACHE does not provide anything better that sequential access,
  besides, only a single write is mutex-protected, which is not suitable,
  since we should write a transaction atomically.

  To solve this, a special layer on top Event_log is implemented.
  There are two IO_CACHE files underneath: one for reading, and one for
  writing.

  Once the read cache is empty, an exclusive lock is acquired (we can wait
  for a currently active transaction finish writing), and flip() is emitted,
  i.e. the write cache is reopened for read, and the read cache is emptied,
  and reopened for writing.

  This reminds a buffer flip that happens in accelerated graphics
  (DirectX/OpenGL/etc).

  Cache_flip_event_log is considered non-blocking for a single reader and a
  single writer in this sense, with the only lock held by reader during flip.

  An alternative approach by implementing a fair concurrent circular buffer
  is described in MDEV-24676.

* Cache managers:
  We have two cache sinks: statement and transactional.
  It is important that the changes are first cached per-statement and
  per-transaction.
  If a statement fails, then only statement data is rolled back. The
  transaction moves along, however.

  Turns out, there's no guarantee that TABLE well persist in
  thd->open_tables to the transaction commit moment.
  If an error occurs, tables from statement are purged.
  Therefore, we can't store te caches in TABLE. Ideally, it should be
  handlerton, but we cut the corner and store it in THD in a list.

1 files changed, 5 insertions, 1 deletions

diff --git a/sql/log_event.h b/sql/log_event.h
index ad8ddb3deac..ee91a103287 100644
--- a/sql/log_event.h
+++ b/sql/log_event.h
@@ -3742,6 +3742,8 @@ private:
   bool  m_used_query_txt;
 };
 
+class table_def;
+
 /**
   @class Table_map_log_event
 
@@ -4393,6 +4395,7 @@ public:
   virtual bool print(FILE *file, PRINT_EVENT_INFO *print_event_info);
 #endif
 
+  table_def get_table_def();
 
 private:
 #if defined(MYSQL_SERVER) && defined(HAVE_REPLICATION)
@@ -4697,7 +4700,7 @@ protected:
 #endif
   ulonglong       m_table_id;	/* Table ID */
   MY_BITMAP   m_cols;		/* Bitmap denoting columns available */
-  ulong       m_width;          /* The width of the columns bitmap */
+  uint        m_width;          /* The width of the columns bitmap */
   /*
     Bitmap for columns available in the after image, if present. These
     fields are only available for Update_rows events. Observe that the
@@ -4732,6 +4735,7 @@ protected:
 
   /* helper functions */
 
+
 #if defined(MYSQL_SERVER) && defined(HAVE_REPLICATION)
   const uchar *m_curr_row;     /* Start of the row being processed */
   const uchar *m_curr_row_end; /* One-after the end of the current row */