WL#3281: Handler cleanup 2006

Cleanup of handler / handlerton structures to make the interfaces more efficent
and stable.
(Some of these changes are required for Falcon, Maria and Solid to work more
efficently)

Note that the proposed changes are not complete and there may modification
to the work while the changes are done.

Suggested handler changes (see LLD for actual changes made):

- Rip out all 'ha_get_bit' and 'ha_set_bit' and related functions from
  handler.h and replace these with a function that sets and signals
  column map changes:

  void column_bitmaps_set(MY_BITMAP *read_set_arg, MY_BITMAP *write_set_arg)
  virtual void column_bitmaps_signal();

  The reason for this is that MySQL can during one operation do
  want to read a record in several stages, but with different
  set of fields (for example with sorting, min-max optimization, range
  read etc) and the current schema is thus not scalable.
  (Having one function for each bitmap is also very inefficient).
  The bitmaps should be manipualted in the TABLE structure and not in
  the handler structure (for the above reason).

  The plan is to pre-allocate 3 bitmaps in the table structure, one
  for read, one for write and one for temporary things, like filesort.

- Fix ha_retrieve_all_kp() and related function as the current implementation
  forces handler that don't need PK to re-retrieve a row to have to fetch
  the row, even in an index read)

- Remove duplicate fields from handlerton/plugin

- Clean up initialization of handlerton so that we can add new
  elements to it without having to do any changes to existing storage
  engines. One implication of this is that the handlerton structures is
  prefilled by a global handlerton init function and then sent to the
  handler to be filled up.

- Define that ha_reset() should reset all things like it would
  be after open. (Ie, call ha_index_or_rnd_end(), reset key usage etc)
  In other words, there should be no need to call things like
  extra(HA_EXTRA_NO_KEYREAD) anymore.

  One requried change for this is that we have to call 'reset()' for all locked
  tables in 'close_thread_tables'

- Potentially remove one or all of the 'extra(HA_EXTRA_KEYREAD)' and
  extra(HA_EXTRA_RETRIEVE_ALL_COLS) calls as they are not
  strictly necessary anymore when we have bitmaps for fields.

  (Don't yet know how to remove HA_EXTRA_KEYREAD to not slow down
  MyISAM)

- New ways to do auto_increment handling, so that we can avoid locks
  while inserting rows.  (We need functions to allocate and free a region
  of auto-increment values).  This will make statement based logging
  faster as we need fewer locks.  WL#3146
  (Guilhem will probabably do this part)

- Change statement based binary log to handle the new auto-increment

  handling (part of WL#3146)

- Extend the possible index and row types. (enum changes)

- Add virtual function that will return 0/1 based on the fact if the
  error was fatal or not (Ie, if INSERT IGNORE can ignore the error)
  (This may already be done)

- New interface of index_read() to be able to handle bitmap indexes
  (Need to change length of key to bitmap to say which key parts are
  available)

- New interface to tell MySQL which log files can be purged. WL#3073
  (Sanja will probably do this part)

- New interface for retrieving log information. WL#3073
  (part of above task)

- Fix all parts of MySQL to set the bitmaps properly.

- Move all 'statistics' variables from 'handler' base class to
  a structure (in the base class). This will make it easier to
  know what are statistic variables and what are internal variables.

- Add a hash of all tables used by any active transaction. We need
  this to not drop or rename a table or database while an object is
  still in use.  (Currently we only detect if a table is in use by a
  running statement)

- Change how table->sort.io_cache is handled (check free_io_cache() usage)
  (Now it's a hack that can lead to potential errors)

- Add command line option support to handler code.
  WL#2937 describes this. (Jimw may be the implementor of this)

- All handler to add an settable variables.

- Move condition pushdown from THD to be engine specific.

- implicite_emptied should be made a virtual function and not be
  and object in all handlers.

- New handler startup methods. We want first to initialize all
  handlers and potentially do recovery with all available resources
  and then start them up. (This is to get faster startup after crash).

- More arguments to ha_panic() to implement more engine shutdown
  methods.  (Needed by graceful shutdown patch)

- Move the code that *every* handler should do from virtual functions to
  ha_ wrappers. E.g. create a non-virtual ha_write_row(), and let it
  update auto increment, timestamps, status_vars, and call virtual
  write_row() which is private. Same for all virtual functions that update
  status_vars.

- Allocate an optional THR_LOCK_DATA structure in TABLE and THR_LOCK in
TABLE_SHARE   to be able to create a default virtual store_lock() method to
simplify locking for storage handlers.

- Don't call store_lock() with option TL_IGNORE anymore. Also ensure we only
call it when the table is not locked (ie, we can remove the test of lock.type ==
TL_UNLOCK)

This worklog item was done more in a spirit 'as much as possible in
given time' than 'get everything done' as we have a need to get 5.1
stable ASAP.

Here is what was done in 5.1 server as part of this worklog task: (I
will shortly create a new worklog item with changes that was listed in
this worklog entry but not done).
(Yes, this is a bit against the nature of a worklog item, where you should
plan things first in detail before implementing it instead of writing what
was done after the fact, but in this case I didn't have much choice because
of the time constraints).

Changes done that requires code changes in code of other storage engines:
(Note that all changes are very straightforward and one should find all issues
by compiling a --debug build and fixing all compiler errors and all
asserts in field.cc while running the test suite),

- New optional handler function introduced: reset()
  This is called after every DML statement to make it easy for a handler to
  statement specific cleanups.
  (The only case it's not called is if force the file to be closed)

- handler::extra(HA_EXTRA_RESET) is removed. Code that was there before
  should be moved to handler::reset()

- table->read_set contains a bitmap over all columns that are needed
  in the query.  read_row() and similar functions only needs to read these
  columns
- table->write_set contains a bitmap over all columns that will be updated
  in the query. write_row() and update_row() only needs to update these
  columns.
  The above bitmaps should now be up to date in all context
  (including ALTER TABLE, filesort()).

  The handler is informed of any changes to the bitmap after
  fix_fields() by calling the virtual function
  handler::column_bitmaps_signal(). If the handler does caching of
  these bitmaps (instead of using table->read_set, table->write_set),
  it should redo the caching in this code. as the signal() may be sent
  several times, it's probably best to set a variable in the signal
  and redo the caching on read_row() / write_row() if the variable was
  set.

- Removed the read_set and write_set bitmap objects from the handler class

- Removed all column bit handling functions from the handler class.
  (Now one instead uses the normal bitmap functions in my_bitmap.c instead
  of handler dedicated bitmap functions)

- field->query_id is removed. One should instead instead check
  table->read_set and table->write_set if a field is used in the query.

- handler::extra(HA_EXTRA_RETRIVE_ALL_COLS) and
  handler::extra(HA_EXTRA_RETRIEVE_PRIMARY_KEY) are removed. One should now
  instead use table->read_set to check for which columns to retrieve.

- If a handler needs to call Field->val() or Field->store() on columns
  that are not used in the query, one should install a temporary
  all-columns-used map while doing so. For this, we provide the following
  functions:

  my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->read_set);
  field->val();
  dbug_tmp_restore_column_map(table->read_set, old_map);

  and similar for the write map:

  my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->write_set);
  field->val();
  dbug_tmp_restore_column_map(table->write_set, old_map);

  If this is not done, you will sooner or later hit a DBUG_ASSERT
  in the field store() / val() functions.
  (For not DBUG binaries, the dbug_tmp_restore_column_map() and
  dbug_tmp_restore_column_map() are inline dummy functions and should
  be optimized away be the compiler).

- If one needs to temporary set the column map for all binaries (and not
  just to avoid the DBUG_ASSERT() in the Field::store() / Field::val()
  methods) one should use the functions tmp_use_all_columns() and
  tmp_restore_column_map() instead of the above dbug_ variants.

- All 'status' fields in the handler base class (like records,
  data_file_length etc) are now stored in a 'stats' struct. This makes
  it easier to know what status variables are provided by the base
  handler.  This requires some trivial variable names in the extra()
  function.

- New virtual function handler::records().  This is called to optimize
  COUNT(*) if (handler::table_flags() & HA_HAS_RECORDS()) is true.
  (stats.records is not supposed to be an exact value. It's only has to
  be 'reasonable enough' for the optimizer to be able to choose a good
  optimization path).

- Non virtual handler::init() function added for caching of virtual
  constants from engine.

- Removed has_transactions() virtual method. Now one should instead return
  HA_NO_TRANSACTIONS in table_flags() if the table handler DOES NOT support
  transactions.

- The 'xxxx_create_handler()' function now has a MEM_ROOT_root argument
  that is to be used with 'new handler_name()' to allocate the handler
  in the right area.  The xxxx_create_handler() function is also
  responsible for any initialization of the object before returning.

  For example, one should change:

  static handler *myisam_create_handler(TABLE_SHARE *table)
  {
    return new ha_myisam(table);
  }

  ->

  static handler *myisam_create_handler(TABLE_SHARE *table, MEM_ROOT *mem_root)
  {
    return new (mem_root) ha_myisam(table);
  }

- New optional virtual function: use_hidden_primary_key().
  This is called in case of an update/delete when
  (table_flags() and HA_PRIMARY_KEY_REQUIRED_FOR_DELETE) is defined
  but we don't have a primary key. This allows the handler to take precisions
  in remembering any hidden primary key to able to update/delete any
  found row. The default handler marks all columns to be read.

- handler::table_flags() now returns a ulonglong (to allow for more flags).

- New/changed table_flags()
  - HA_HAS_RECORDS	    Set if ::records() is supported
  - HA_NO_TRANSACTIONS	    Set if engine doesn't support transactions
  - HA_PRIMARY_KEY_REQUIRED_FOR_DELETE
                            Set if we should mark all primary key columns for
			    read when reading rows as part of a DELETE
			    statement. If there is no primary key,
			    all columns are marked for read.
  - HA_PARTIAL_COLUMN_READ  Set if engine will not read all columns in some
			    cases (based on table->read_set)
 - HA_PRIMARY_KEY_ALLOW_RANDOM_ACCESS
   			    Renamed to HA_PRIMARY_KEY_REQUIRED_FOR_POSITION.
 - HA_DUPP_POS              Renamed to HA_DUPLICATE_POS
 - HA_REQUIRES_KEY_COLUMNS_FOR_DELETE
			    Set this if we should mark ALL key columns for
			    read when when reading rows as part of a DELETE
			    statement. In case of an update we will mark
			    all keys for read for which key part changed
			    value.
  - HA_STATS_RECORDS_IS_EXACT
			     Set this if stats.records is exact.
			     (This saves us some extra records() calls
			     when optimizing COUNT(*))
			    

- Removed table_flags()
  - HA_NOT_EXACT_COUNT     Now one should instead use HA_HAS_RECORDS if
			   handler::records() gives an exact count() and
			   HA_STATS_RECORDS_IS_EXACT if stats.records is exact.
  - HA_READ_RND_SAME	   Removed (no one supported this one)

- Removed not needed functions ha_retrieve_all_cols() and ha_retrieve_all_pk()

- Renamed handler::dupp_pos to handler::dup_pos

- Removed not used variable handler::sortkey


Upper level handler changes:

- ha_reset() now does some overall checks and calls ::reset()
- ha_table_flags() added. This is a cached version of table_flags(). The
  cache is updated on engine creation time and updated on open.


MySQL level changes (not obvious from the above):

- DBUG_ASSERT() added to check that column usage matches what is set
  in the column usage bit maps. (This found a LOT of bugs in current
  column marking code).

- In 5.1 before, all used columns was marked in read_set and only updated
  columns was marked in write_set. Now we only mark columns for which we
  need a value in read_set.

- Column bitmaps are created in open_binary_frm() and open_table_from_share().
  (Before this was in table.cc)

- handler::table_flags() calls are replaced with handler::ha_table_flags()

- For calling field->val() you must have the corresponding bit set in
  table->read_set. For calling field->store() you must have the
  corresponding bit set in table->write_set. (There are asserts in
  all store()/val() functions to catch wrong usage)

- thd->set_query_id is renamed to thd->mark_used_columns and instead
  of setting this to an integer value, this has now the values:
  MARK_COLUMNS_NONE, MARK_COLUMNS_READ, MARK_COLUMNS_WRITE
  Changed also all variables named 'set_query_id' to mark_used_columns.

- In filesort() we now inform the handler of exactly which columns are needed
  doing the sort and choosing the rows.

- The TABLE_SHARE object has a 'all_set' column bitmap one can use
  when one needs a column bitmap with all columns set.
  (This is used for table->use_all_columns() and other places)

- The TABLE object has 3 column bitmaps:
  - def_read_set     Default bitmap for columns to be read
  - def_write_set    Default bitmap for columns to be written
  - tmp_set          Can be used as a temporary bitmap when needed.
  The table object has also two pointer to bitmaps read_set and write_set
  that the handler should use to find out which columns are used in which way.

- count() optimization now calls handler::records() instead of using
  handler->stats.records (if (table_flags() & HA_HAS_RECORDS) is true).

- Added extra argument to Item::walk() to indicate if we should also
  traverse sub queries.

- Added TABLE parameter to cp_buffer_from_ref()

- Don't close tables created with CREATE ... SELECT but keep them in
  the table cache. (Faster usage of newly created tables).


New interfaces:

- table->clear_column_bitmaps() to initialize the bitmaps for tables
  at start of new statements.

- table->column_bitmaps_set() to set up new column bitmaps and signal
  the handler about this.

- table->column_bitmaps_set_no_signal() for some few cases where we need
  to setup new column bitmaps but don't signal the handler (as the handler
  has already been signaled about these before). Used for the momement
  only in opt_range.cc when doing ROR scans.

- table->use_all_columns() to install a bitmap where all columns are marked
  as use in the read and the write set.

- table->default_column_bitmaps() to install the normal read and write
  column bitmaps, but not signaling the handler about this.
  This is mainly used when creating TABLE instances.

- table->mark_columns_needed_for_delete(),
  table->mark_columns_needed_for_delete() and
  table->mark_columns_needed_for_insert() to allow us to put additional
  columns in column usage maps if handler so requires.
  (The handler indicates what it neads in handler->table_flags())

- table->prepare_for_position() to allow us to tell handler that it
  needs to read primary key parts to be able to store them in
  future table->position() calls.
  (This replaces the table->file->ha_retrieve_all_pk function)

- table->mark_auto_increment_column() to tell handler are going to update
  columns part of any auto_increment key.

- table->mark_columns_used_by_index() to mark all columns that is part of
  an index.  It will also send extra(HA_EXTRA_KEYREAD) to handler to allow
  it to quickly know that it only needs to read colums that are part
  of the key.  (The handler can also use the column map for detecting this,
  but simpler/faster handler can just monitor the extra() call).

- table->mark_columns_used_by_index_no_reset() to in addition to other columns,
  also mark all columns that is used by the given key.

- table->restore_column_maps_after_mark_index() to restore to default
  column maps after a call to table->mark_columns_used_by_index().

- New item function register_field_in_read_map(), for marking used columns
  in table->read_map. Used by filesort() to mark all used columns

- Maintain in TABLE->merge_keys set of all keys that are used in query.
  (Simplices some optimization loops)

- Maintain Field->part_of_key_not_clustered which is like Field->part_of_key
  but the field in the clustered key is not assumed to be part of all index.
  (used in opt_range.cc for faster loops)

-  dbug_tmp_use_all_columns(), dbug_tmp_restore_column_map()
   tmp_use_all_columns() and tmp_restore_column_map() functions to temporally
   mark all columns as usable.  The 'dbug_' version is primarily intended
   inside a handler when it wants to just call Field:store() & Field::val()
   functions, but don't need the column maps set for any other usage.
   (ie:: bitmap_is_set() is never called)

- We can't use compare_records() to skip updates for handlers that returns
  a partial column set and the read_set doesn't cover all columns in the
  write set. The reason for this is that if we have a column marked only for
  write we can't in the MySQL level know if the value changed or not.
  The reason this worked before was that MySQL marked all to be written
  columns as also to be read. The new 'optimal' bitmaps exposed this 'hidden
  bug'.

- open_table_from_share() does not anymore setup temporary MEM_ROOT
  object as a thread specific variable for the handler. Instead we
  send the to-be-used MEMROOT to get_new_handler().
  (Simpler, faster code)



Bugs fixed:

- Column marking was not done correctly in a lot of cases.
  (ALTER TABLE, when using triggers, auto_increment fields etc)
  (Could potentially result in wrong values inserted in table handlers
  relying on that the old column maps or field->set_query_id was correct)
  Especially when it comes to triggers, there may be cases where the
  old code would cause lost/wrong values for NDB and/or InnoDB tables.

- Split thd->options flag OPTION_STATUS_NO_TRANS_UPDATE to two flags:
  OPTION_STATUS_NO_TRANS_UPDATE and OPTION_KEEP_LOG.
  This allowed me to remove some wrong warnings about:
  "Some non-transactional changed tables couldn't be rolled back"

- Fixed handling of INSERT .. SELECT and CREATE ... SELECT that wrongly reset
  (thd->options & OPTION_STATUS_NO_TRANS_UPDATE) which caused us to loose
  some warnings about
  "Some non-transactional changed tables couldn't be rolled back")

- Fixed use of uninitialized memory in ha_ndbcluster.cc::delete_table()
  which could cause delete_table to report random failures.

- Fixed core dumps for some tests when running with --debug

- Added missing FN_LIBCHAR in mysql_rm_tmp_tables()
  (This has probably caused us to not properly remove temporary files after
  crash)

- slow_logs was not properly initialized, which could maybe cause
  extra/lost entries in slow log.

- If we get an duplicate row on insert, change column map to read and
  write all columns while retrying the operation. This is required by
  the definition of REPLACE and also ensures that fields that are only
  part of UPDATE are properly handled.  This fixed a bug in NDB and
  REPLACE where REPLACE wrongly copied some column values from the replaced
  row.

- For table handler that doesn't support NULL in keys, we would give an error
  when creating a primary key with NULL fields, even after the fields has been
  automaticly converted to NOT NULL.

- Creating a primary key on a SPATIAL key, would fail if field was not
  declared as NOT NULL.


Cleanups:

- Removed not used condition argument to setup_tables

- Removed not needed item function reset_query_id_processor().

- Field->add_index is removed. Now this is instead maintained in
  (field->flags & FIELD_IN_ADD_INDEX)

- Field->fieldnr is removed (use field->field_index instead)

- New argument to filesort() to indicate that it should return a set of
  row pointers (not used columns). This allowed me to remove some references
  to sql_command in filesort and should also enable us to return column
  results in some cases where we couldn't before.

- Changed column bitmap handling in opt_range.cc to be aligned with TABLE
  bitmap, which allowed me to use bitmap functions instead of looping over
  all fields to create some needed bitmaps. (Faster and smaller code)

- Broke up found too long lines

- Moved some variable declaration at start of function for better code
  readability.

- Removed some not used arguments from functions.
  (setup_fields(), mysql_prepare_insert_check_table())

- setup_fields() now takes an enum instead of an int for marking columns
   usage.

- For internal temporary tables, use handler::write_row(),
  handler::delete_row() and handler::update_row() instead of
  handler::ha_xxxx() for faster execution.

- Changed some constants to enum's and define's.

- Using separate column read and write sets allows for easier checking
  of timestamp field was set by statement.

- Remove calls to free_io_cache() as this is now done automaticly in ha_reset()

- Don't build table->normalized_path as this is now identical to table->path
  (after bar's fixes to convert filenames)

- Fixed some missed DBUG_PRINT(.."%lx") to use "0x%lx" to make it easier to
  do comparision with the 'convert-dbug-for-diff' tool.


Things left to do in 5.1:

- We wrongly log failed CREATE TABLE ... SELECT in some cases when using
  row based logging (as shown by testcase binlog_row_mix_innodb_myisam.result)
  Mats has promised to look into this.

- Test that my fix for CREATE TABLE ... SELECT is indeed correct.
  (I added several test cases for this, but in this case it's better that
  someone else also tests this throughly).
  Lars has promosed to do this.

- Update worklog #WL3281 with things that where not done in this cleanup.
  What is should still be done in 5.1 are:

 - Add a hash of all tables used by any active transaction. We need
   this to not drop or rename a table or database while an object is
   still in use.  (Currently we only detect if a table is in use by a
   running statement)

 - Maybe: New interface of index_read() to be able to handle bitmap indexes
   (Need to change length of key to bitmap to say which key parts are
   available)