MDEV-12353 preparation: Clean up mtr_t

mtr_t::Impl, mtr_t::Command: Merge to mtr_t.

MTR_MAGIC_N: Remove.

MTR_STATE_COMMITTING: Remove. This state was only being set
internally during mtr_t::commit().

mtr_t::Command::m_locks_released: Remove (set-and-never-read member).

mtr_t::Command::m_start_lsn: Replaced with the return value of
finish_write() and a parameter to release_blocks().

mtr_t::Command::m_end_lsn: Removed as a duplicate of mtr_t::m_commit_lsn.

mtr_t::Command::prepare_write(): Replace a switch () with a
comparison against 0. Only 2 m_log_mode are allowed.

4 files changed, 254 insertions, 495 deletions

diff --git a/storage/innobase/include/mtr0mtr.h b/storage/innobase/include/mtr0mtr.h
index 4f518071bfb..30d2e937f1f 100644
--- a/storage/innobase/include/mtr0mtr.h
+++ b/storage/innobase/include/mtr0mtr.h
@@ -2,7 +2,7 @@
 
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2013, 2018, MariaDB Corporation.
+Copyright (c) 2013, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -146,68 +146,7 @@ struct mtr_memo_slot_t {
 
 /** Mini-transaction handle and buffer */
 struct mtr_t {
-
-	/** State variables of the mtr */
-	struct Impl {
-
-		/** memo stack for locks etc. */
-		mtr_buf_t	m_memo;
-
-		/** mini-transaction log */
-		mtr_buf_t	m_log;
-
-		/** true if mtr has made at least one buffer pool page dirty */
-		bool		m_made_dirty;
-
-		/** true if inside ibuf changes */
-		bool		m_inside_ibuf;
-
-		/** true if the mini-transaction modified buffer pool pages */
-		bool		m_modifications;
-
-		/** Count of how many page initial log records have been
-		written to the mtr log */
-		ib_uint32_t	m_n_log_recs;
-
-		/** specifies which operations should be logged; default
-		value MTR_LOG_ALL */
-		mtr_log_t	m_log_mode;
-#ifdef UNIV_DEBUG
-		/** Persistent user tablespace associated with the
-		mini-transaction, or 0 (TRX_SYS_SPACE) if none yet */
-		ulint		m_user_space_id;
-#endif /* UNIV_DEBUG */
-		/** User tablespace that is being modified by the
-		mini-transaction */
-		fil_space_t*	m_user_space;
-		/** Undo tablespace that is being modified by the
-		mini-transaction */
-		fil_space_t*	m_undo_space;
-		/** System tablespace if it is being modified by the
-		mini-transaction */
-		fil_space_t*	m_sys_space;
-
-		/** State of the transaction */
-		mtr_state_t	m_state;
-
-		/** Flush Observer */
-		FlushObserver*	m_flush_observer;
-
-#ifdef UNIV_DEBUG
-		/** For checking corruption. */
-		ulint		m_magic_n;
-#endif /* UNIV_DEBUG */
-
-		/** Owning mini-transaction */
-		mtr_t*		m_mtr;
-	};
-
-	mtr_t()
-	{
-		m_impl.m_state = MTR_STATE_INIT;
-	}
-
-	~mtr_t() { }
+	mtr_t() : m_state(MTR_STATE_INIT) {}
 
 	/** Release the free extents that was reserved using
 	fsp_reserve_free_extents().  This is equivalent to calling
@@ -236,14 +175,7 @@ struct mtr_t {
 
 	/** Return current size of the buffer.
 	@return	savepoint */
-	ulint get_savepoint() const
-		MY_ATTRIBUTE((warn_unused_result))
-	{
-		ut_ad(is_active());
-		ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-
-		return(m_impl.m_memo.size());
-	}
+	ulint get_savepoint() const {ut_ad(is_active()); return m_memo.size();}
 
 	/** Release the (index tree) s-latch stored in an mtr memo after a
 	savepoint.
@@ -279,10 +211,10 @@ struct mtr_t {
 	@return the system tablespace */
 	fil_space_t* set_sys_modified()
 	{
-		if (!m_impl.m_sys_space) {
+		if (!m_sys_space) {
 			lookup_sys_space();
 		}
-		return(m_impl.m_sys_space);
+		return m_sys_space;
 	}
 
 	/** Copy the tablespaces associated with the mini-transaction
@@ -291,15 +223,15 @@ struct mtr_t {
 	the same set of tablespaces as this one */
 	void set_spaces(const mtr_t& mtr)
 	{
-		ut_ad(!m_impl.m_user_space_id);
-		ut_ad(!m_impl.m_user_space);
-		ut_ad(!m_impl.m_undo_space);
-		ut_ad(!m_impl.m_sys_space);
-
-		ut_d(m_impl.m_user_space_id = mtr.m_impl.m_user_space_id);
-		m_impl.m_user_space = mtr.m_impl.m_user_space;
-		m_impl.m_undo_space = mtr.m_impl.m_undo_space;
-		m_impl.m_sys_space = mtr.m_impl.m_sys_space;
+		ut_ad(!m_user_space_id);
+		ut_ad(!m_user_space);
+		ut_ad(!m_undo_space);
+		ut_ad(!m_sys_space);
+
+		ut_d(m_user_space_id = mtr.m_user_space_id);
+		m_user_space = mtr.m_user_space;
+		m_undo_space = mtr.m_undo_space;
+		m_sys_space = mtr.m_sys_space;
 	}
 
 	/** Set the tablespace associated with the mini-transaction
@@ -308,13 +240,13 @@ struct mtr_t {
 	@return	the tablespace */
 	fil_space_t* set_named_space(ulint space_id)
 	{
-		ut_ad(!m_impl.m_user_space_id);
-		ut_d(m_impl.m_user_space_id = space_id);
+		ut_ad(!m_user_space_id);
+		ut_d(m_user_space_id = space_id);
 		if (!space_id) {
 			return(set_sys_modified());
 		} else {
 			lookup_user_space(space_id);
-			return(m_impl.m_user_space);
+			return m_user_space;
 		}
 	}
 
@@ -381,18 +313,12 @@ struct mtr_t {
 	void release_page(const void* ptr, mtr_memo_type_t type);
 
 	/** Note that the mini-transaction has modified data. */
-	void set_modified()
-	{
-		m_impl.m_modifications = true;
-	}
+	void set_modified() { m_modifications = true; }
 
 	/** Set the state to not-modified. This will not log the
 	changes.  This is only used during redo log apply, to avoid
 	logging the changes. */
-	void discard_modifications()
-	{
-		m_impl.m_modifications = false;
-	}
+	void discard_modifications() { m_modifications = false; }
 
 	/** Get the LSN of commit().
 	@return the commit LSN
@@ -404,45 +330,28 @@ struct mtr_t {
 	}
 
 	/** Note that we are inside the change buffer code. */
-	void enter_ibuf()
-	{
-		m_impl.m_inside_ibuf = true;
-	}
+	void enter_ibuf() { m_inside_ibuf = true; }
 
 	/** Note that we have exited from the change buffer code. */
-	void exit_ibuf()
-	{
-		m_impl.m_inside_ibuf = false;
-	}
+	void exit_ibuf() { m_inside_ibuf = false; }
 
 	/** @return true if we are inside the change buffer code */
-	bool is_inside_ibuf() const
-	{
-		return(m_impl.m_inside_ibuf);
-	}
+	bool is_inside_ibuf() const { return m_inside_ibuf; }
 
 	/*
 	@return true if the mini-transaction is active */
-	bool is_active() const
-	{
-		return(m_impl.m_state == MTR_STATE_ACTIVE);
-	}
+	bool is_active() const { return m_state == MTR_STATE_ACTIVE; }
 
 	/** Get flush observer
 	@return flush observer */
-	FlushObserver* get_flush_observer() const
-	{
-		return(m_impl.m_flush_observer);
-	}
+	FlushObserver* get_flush_observer() const { return m_flush_observer; }
 
 	/** Set flush observer
 	@param[in]	observer	flush observer */
 	void set_flush_observer(FlushObserver*	observer)
 	{
-		ut_ad(observer == NULL
-		      || m_impl.m_log_mode == MTR_LOG_NO_REDO);
-
-		m_impl.m_flush_observer = observer;
+		ut_ad(observer == NULL || m_log_mode == MTR_LOG_NO_REDO);
+		m_flush_observer = observer;
 	}
 
 #ifdef UNIV_DEBUG
@@ -482,65 +391,31 @@ struct mtr_t {
 	void print() const;
 
 	/** @return true if the mini-transaction has committed */
-	bool has_committed() const
-	{
-		return(m_impl.m_state == MTR_STATE_COMMITTED);
-	}
-
-	/** @return true if the mini-transaction is committing */
-	bool is_committing() const
-	{
-		return(m_impl.m_state == MTR_STATE_COMMITTING);
-	}
+	bool has_committed() const { return m_state == MTR_STATE_COMMITTED; }
 
 	/** @return true if mini-transaction contains modifications. */
-	bool has_modifications() const
-	{
-		return(m_impl.m_modifications);
-	}
+	bool has_modifications() const { return m_modifications; }
 
 	/** @return the memo stack */
-	const mtr_buf_t* get_memo() const
-	{
-		return(&m_impl.m_memo);
-	}
+	const mtr_buf_t* get_memo() const { return &m_memo; }
 
 	/** @return the memo stack */
-	mtr_buf_t* get_memo()
-	{
-		return(&m_impl.m_memo);
-	}
+	mtr_buf_t* get_memo() { return &m_memo; }
 #endif /* UNIV_DEBUG */
 
 	/** @return true if a record was added to the mini-transaction */
-	bool is_dirty() const
-	{
-		return(m_impl.m_made_dirty);
-	}
+	bool is_dirty() const { return m_made_dirty; }
 
 	/** Note that a record has been added to the log */
-	void added_rec()
-	{
-		++m_impl.m_n_log_recs;
-	}
+	void added_rec() { ++m_n_log_recs; }
 
 	/** Get the buffered redo log of this mini-transaction.
 	@return	redo log */
-	const mtr_buf_t* get_log() const
-	{
-		ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-
-		return(&m_impl.m_log);
-	}
+	const mtr_buf_t* get_log() const { return &m_log; }
 
 	/** Get the buffered redo log of this mini-transaction.
 	@return	redo log */
-	mtr_buf_t* get_log()
-	{
-		ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-
-		return(&m_impl.m_log);
-	}
+	mtr_buf_t* get_log() { return &m_log; }
 
 	/** Push an object to an mtr memo stack.
 	@param object	object
@@ -560,15 +435,60 @@ private:
 	@param[in]	space_id	tablespace ID  */
 	void lookup_user_space(ulint space_id);
 
-	class Command;
+	/** Prepare to write the mini-transaction log to the redo log buffer.
+	@return number of bytes to write in finish_write() */
+	inline ulint prepare_write();
 
-	friend class Command;
+	/** Append the redo log records to the redo log buffer.
+	@param[in]	len	number of bytes to write
+	@return start_lsn */
+	inline lsn_t finish_write(ulint len);
 
-private:
-	Impl			m_impl;
+	/** Release the resources */
+	inline void release_resources();
+
+	/** memo stack for locks etc. */
+	mtr_buf_t	m_memo;
+
+	/** mini-transaction log */
+	mtr_buf_t	m_log;
+
+	/** true if mtr has made at least one buffer pool page dirty */
+	bool		m_made_dirty;
+
+	/** true if inside ibuf changes */
+	bool		m_inside_ibuf;
+
+	/** true if the mini-transaction modified buffer pool pages */
+	bool		m_modifications;
+
+	/** Count of how many page initial log records have been
+	written to the mtr log */
+	ib_uint32_t	m_n_log_recs;
+
+	/** specifies which operations should be logged; default
+	value MTR_LOG_ALL */
+	mtr_log_t	m_log_mode;
+#ifdef UNIV_DEBUG
+	/** Persistent user tablespace associated with the
+	mini-transaction, or 0 (TRX_SYS_SPACE) if none yet */
+	ulint		m_user_space_id;
+#endif /* UNIV_DEBUG */
+	/** User tablespace that is being modified by the mini-transaction */
+	fil_space_t*	m_user_space;
+	/** Undo tablespace that is being modified by the mini-transaction */
+	fil_space_t*	m_undo_space;
+	/** System tablespace if being modified by the mini-transaction */
+	fil_space_t*	m_sys_space;
+
+	/** State of the transaction */
+	mtr_state_t	m_state;
+
+	/** Flush Observer */
+	FlushObserver*	m_flush_observer;
 
 	/** LSN at commit time */
-	volatile lsn_t		m_commit_lsn;
+	lsn_t		m_commit_lsn;
 };
 
 #include "mtr0mtr.ic"
diff --git a/storage/innobase/include/mtr0mtr.ic b/storage/innobase/include/mtr0mtr.ic
index 574d0de24a5..7175ede0d6a 100644
--- a/storage/innobase/include/mtr0mtr.ic
+++ b/storage/innobase/include/mtr0mtr.ic
@@ -49,7 +49,6 @@ mtr_t::memo_push(void* object, mtr_memo_type_t type)
 	ut_ad(object != NULL);
 	ut_ad(type >= MTR_MEMO_PAGE_S_FIX);
 	ut_ad(type <= MTR_MEMO_SX_LOCK);
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
 	ut_ad(ut_is_2pow(type));
 
 	/* If this mtr has x-fixed a clean page then we set
@@ -58,15 +57,13 @@ mtr_t::memo_push(void* object, mtr_memo_type_t type)
 	can insert the dirtied page to the flush list. */
 
 	if ((type == MTR_MEMO_PAGE_X_FIX || type == MTR_MEMO_PAGE_SX_FIX)
-	    && !m_impl.m_made_dirty) {
+	    && !m_made_dirty) {
 
-		m_impl.m_made_dirty = is_block_dirtied(
+		m_made_dirty = is_block_dirtied(
 			reinterpret_cast<const buf_block_t*>(object));
 	}
 
-	mtr_memo_slot_t*	slot;
-
-	slot = m_impl.m_memo.push<mtr_memo_slot_t*>(sizeof(*slot));
+	mtr_memo_slot_t* slot = m_memo.push<mtr_memo_slot_t*>(sizeof(*slot));
 
 	slot->type = type;
 	slot->object = object;
@@ -81,11 +78,9 @@ mtr_t::release_s_latch_at_savepoint(
 	rw_lock_t*	lock)
 {
 	ut_ad(is_active());
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-
-	ut_ad(m_impl.m_memo.size() > savepoint);
+	ut_ad(m_memo.size() > savepoint);
 
-	mtr_memo_slot_t* slot = m_impl.m_memo.at<mtr_memo_slot_t*>(savepoint);
+	mtr_memo_slot_t* slot = m_memo.at<mtr_memo_slot_t*>(savepoint);
 
 	ut_ad(slot->object == lock);
 	ut_ad(slot->type == MTR_MEMO_S_LOCK);
@@ -104,8 +99,7 @@ mtr_t::sx_latch_at_savepoint(
 	buf_block_t*	block)
 {
 	ut_ad(is_active());
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-	ut_ad(m_impl.m_memo.size() > savepoint);
+	ut_ad(m_memo.size() > savepoint);
 
 	ut_ad(!memo_contains_flagged(
 			block,
@@ -113,9 +107,7 @@ mtr_t::sx_latch_at_savepoint(
 			| MTR_MEMO_PAGE_X_FIX
 			| MTR_MEMO_PAGE_SX_FIX));
 
-	mtr_memo_slot_t*	slot;
-
-	slot = m_impl.m_memo.at<mtr_memo_slot_t*>(savepoint);
+	mtr_memo_slot_t* slot = m_memo.at<mtr_memo_slot_t*>(savepoint);
 
 	ut_ad(slot->object == block);
 
@@ -124,8 +116,8 @@ mtr_t::sx_latch_at_savepoint(
 
 	rw_lock_sx_lock(&block->lock);
 
-	if (!m_impl.m_made_dirty) {
-		m_impl.m_made_dirty = is_block_dirtied(block);
+	if (!m_made_dirty) {
+		m_made_dirty = is_block_dirtied(block);
 	}
 
 	slot->type = MTR_MEMO_PAGE_SX_FIX;
@@ -140,8 +132,7 @@ mtr_t::x_latch_at_savepoint(
 	buf_block_t*	block)
 {
 	ut_ad(is_active());
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-	ut_ad(m_impl.m_memo.size() > savepoint);
+	ut_ad(m_memo.size() > savepoint);
 
 	ut_ad(!memo_contains_flagged(
 			block,
@@ -149,9 +140,7 @@ mtr_t::x_latch_at_savepoint(
 			| MTR_MEMO_PAGE_X_FIX
 			| MTR_MEMO_PAGE_SX_FIX));
 
-	mtr_memo_slot_t*	slot;
-
-	slot = m_impl.m_memo.at<mtr_memo_slot_t*>(savepoint);
+	mtr_memo_slot_t* slot = m_memo.at<mtr_memo_slot_t*>(savepoint);
 
 	ut_ad(slot->object == block);
 
@@ -160,8 +149,8 @@ mtr_t::x_latch_at_savepoint(
 
 	rw_lock_x_lock(&block->lock);
 
-	if (!m_impl.m_made_dirty) {
-		m_impl.m_made_dirty = is_block_dirtied(block);
+	if (!m_made_dirty) {
+		m_made_dirty = is_block_dirtied(block);
 	}
 
 	slot->type = MTR_MEMO_PAGE_X_FIX;
@@ -176,11 +165,8 @@ mtr_t::release_block_at_savepoint(
 	buf_block_t*	block)
 {
 	ut_ad(is_active());
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-
-	mtr_memo_slot_t*	slot;
 
-	slot = m_impl.m_memo.at<mtr_memo_slot_t*>(savepoint);
+	mtr_memo_slot_t* slot = m_memo.at<mtr_memo_slot_t*>(savepoint);
 
 	ut_a(slot->object == block);
 
@@ -198,10 +184,10 @@ Gets the logging mode of a mini-transaction.
 mtr_log_t
 mtr_t::get_log_mode() const
 {
-	ut_ad(m_impl.m_log_mode >= MTR_LOG_ALL);
-	ut_ad(m_impl.m_log_mode <= MTR_LOG_SHORT_INSERTS);
+	ut_ad(m_log_mode >= MTR_LOG_ALL);
+	ut_ad(m_log_mode <= MTR_LOG_SHORT_INSERTS);
 
-	return(m_impl.m_log_mode);
+	return m_log_mode;
 }
 
 /**
@@ -214,7 +200,7 @@ mtr_t::set_log_mode(mtr_log_t mode)
 	ut_ad(mode >= MTR_LOG_ALL);
 	ut_ad(mode <= MTR_LOG_SHORT_INSERTS);
 
-	const mtr_log_t	old_mode = m_impl.m_log_mode;
+	const mtr_log_t	old_mode = m_log_mode;
 
 	switch (old_mode) {
 	case MTR_LOG_NO_REDO:
@@ -233,9 +219,8 @@ mtr_t::set_log_mode(mtr_log_t mode)
 	case MTR_LOG_ALL:
 		/* MTR_LOG_NO_REDO can only be set before generating
 		any redo log records. */
-		ut_ad(mode != MTR_LOG_NO_REDO
-		      || m_impl.m_n_log_recs == 0);
-		m_impl.m_log_mode = mode;
+		ut_ad(mode != MTR_LOG_NO_REDO || m_n_log_recs == 0);
+		m_log_mode = mode;
 		return(old_mode);
 	}
 
diff --git a/storage/innobase/include/mtr0types.h b/storage/innobase/include/mtr0types.h
index 1179da6d926..985ad7b81ea 100644
--- a/storage/innobase/include/mtr0types.h
+++ b/storage/innobase/include/mtr0types.h
@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1995, 2015, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, MariaDB Corporation.
+Copyright (c) 2017, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -36,18 +36,18 @@ struct mtr_t;
 /** Logging modes for a mini-transaction */
 enum mtr_log_t {
 	/** Default mode: log all operations modifying disk-based data */
-	MTR_LOG_ALL = 21,
+	MTR_LOG_ALL = 0,
 
 	/** Log no operations and dirty pages are not added to the flush list.
 	Set when applying log in crash recovery or when a modification of a
 	ROW_FORMAT=COMPRESSED page is attempted. */
-	MTR_LOG_NONE = 22,
+	MTR_LOG_NONE,
 
 	/** Don't generate REDO log but add dirty pages to flush list */
-	MTR_LOG_NO_REDO = 23,
+	MTR_LOG_NO_REDO,
 
 	/** Inserts are logged in a shorter form */
-	MTR_LOG_SHORT_INSERTS = 24
+	MTR_LOG_SHORT_INSERTS
 };
 
 /** @name Log item types
@@ -267,15 +267,10 @@ enum mtr_memo_type_t {
 };
 #endif /* !UNIV_CHECKSUM */
 
-#ifdef UNIV_DEBUG
-# define MTR_MAGIC_N		54551
-#endif /* UNIV_DEBUG */
-
 enum mtr_state_t {
 	MTR_STATE_INIT = 0,
-	MTR_STATE_ACTIVE = 12231,
-	MTR_STATE_COMMITTING = 56456,
-	MTR_STATE_COMMITTED = 34676
+	MTR_STATE_ACTIVE,
+	MTR_STATE_COMMITTED
 };
 
 #endif /* mtr0types_h */
diff --git a/storage/innobase/mtr/mtr0mtr.cc b/storage/innobase/mtr/mtr0mtr.cc
index fc6f3321164..533b10b861e 100644
--- a/storage/innobase/mtr/mtr0mtr.cc
+++ b/storage/innobase/mtr/mtr0mtr.cc
@@ -343,6 +343,7 @@ struct ReleaseAll {
 	}
 };
 
+#ifdef UNIV_DEBUG
 /** Check that all slots have been handled. */
 struct DebugCheck {
 	/** @return true always. */
@@ -352,6 +353,7 @@ struct DebugCheck {
 		return(true);
 	}
 };
+#endif
 
 /** Release a resource acquired by the mini-transaction. */
 struct ReleaseBlocks {
@@ -404,59 +406,6 @@ struct ReleaseBlocks {
 	FlushObserver*	m_flush_observer;
 };
 
-class mtr_t::Command {
-public:
-	/** Constructor.
-	Takes ownership of the mtr->m_impl, is responsible for deleting it.
-	@param[in,out]	mtr	mini-transaction */
-	explicit Command(mtr_t* mtr) : m_impl(&mtr->m_impl), m_locks_released()
-	{}
-
-	/** Destructor */
-	~Command()
-	{
-		ut_ad(m_impl == 0);
-	}
-
-	/** Write the redo log record, add dirty pages to the flush list and
-	release the resources. */
-	void execute();
-
-	/** Release the blocks used in this mini-transaction. */
-	void release_blocks();
-
-	/** Release the latches acquired by the mini-transaction. */
-	void release_latches();
-
-	/** Release both the latches and blocks used in the mini-transaction. */
-	void release_all();
-
-	/** Release the resources */
-	void release_resources();
-
-	/** Append the redo log records to the redo log buffer.
-	@param[in]	len	number of bytes to write */
-	void finish_write(ulint len);
-
-private:
-	/** Prepare to write the mini-transaction log to the redo log buffer.
-	@return number of bytes to write in finish_write() */
-	ulint prepare_write();
-
-	/** The mini-transaction state. */
-	mtr_t::Impl*		m_impl;
-
-	/** Set to 1 after the user thread releases the latches. The log
-	writer thread must wait for this to be set to 1. */
-	volatile ulint		m_locks_released;
-
-	/** Start lsn of the possible log entry for this mtr */
-	lsn_t			m_start_lsn;
-
-	/** End lsn of the possible log entry for this mtr */
-	lsn_t			m_end_lsn;
-};
-
 /** Write the block contents to the REDO log */
 struct mtr_write_log_t {
 	/** Append a block to the redo log buffer.
@@ -490,78 +439,77 @@ mtr_write_log(
 /** Start a mini-transaction. */
 void mtr_t::start()
 {
-	UNIV_MEM_INVALID(this, sizeof(*this));
-
-	UNIV_MEM_INVALID(&m_impl, sizeof(m_impl));
-
-	m_commit_lsn = 0;
-
-	new(&m_impl.m_log) mtr_buf_t();
-	new(&m_impl.m_memo) mtr_buf_t();
-
-	m_impl.m_mtr = this;
-	m_impl.m_log_mode = MTR_LOG_ALL;
-	m_impl.m_inside_ibuf = false;
-	m_impl.m_modifications = false;
-	m_impl.m_made_dirty = false;
-	m_impl.m_n_log_recs = 0;
-	m_impl.m_state = MTR_STATE_ACTIVE;
-	ut_d(m_impl.m_user_space_id = TRX_SYS_SPACE);
-	m_impl.m_user_space = NULL;
-	m_impl.m_undo_space = NULL;
-	m_impl.m_sys_space = NULL;
-	m_impl.m_flush_observer = NULL;
-
-	ut_d(m_impl.m_magic_n = MTR_MAGIC_N);
+  UNIV_MEM_INVALID(this, sizeof *this);
+
+  new(&m_memo) mtr_buf_t();
+  new(&m_log) mtr_buf_t();
+
+  m_made_dirty= false;
+  m_inside_ibuf= false;
+  m_modifications= false;
+  m_n_log_recs= 0;
+  m_log_mode= MTR_LOG_ALL;
+  ut_d(m_user_space_id= TRX_SYS_SPACE);
+  m_user_space= NULL;
+  m_undo_space= NULL;
+  m_sys_space= NULL;
+  m_state= MTR_STATE_ACTIVE;
+  m_flush_observer= NULL;
+  m_commit_lsn= 0;
 }
 
 /** Release the resources */
-void
-mtr_t::Command::release_resources()
+inline void mtr_t::release_resources()
 {
-	ut_ad(m_impl->m_magic_n == MTR_MAGIC_N);
-
-	/* Currently only used in commit */
-	ut_ad(m_impl->m_state == MTR_STATE_COMMITTING);
-
-	ut_d(m_impl->m_memo.for_each_block_in_reverse(CIterate<DebugCheck>()));
-
-	/* Reset the mtr buffers */
-	m_impl->m_log.erase();
-
-	m_impl->m_memo.erase();
-
-	m_impl->m_state = MTR_STATE_COMMITTED;
-
-	m_impl = 0;
+  ut_d(m_memo.for_each_block_in_reverse(CIterate<DebugCheck>()));
+  m_log.erase();
+  m_memo.erase();
+  m_state= MTR_STATE_COMMITTED;
 }
 
 /** Commit a mini-transaction. */
 void
 mtr_t::commit()
 {
-	ut_ad(is_active());
-	ut_ad(!is_inside_ibuf());
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-	m_impl.m_state = MTR_STATE_COMMITTING;
+  ut_ad(is_active());
+  ut_ad(!is_inside_ibuf());
 
-	/* This is a dirty read, for debugging. */
-	ut_ad(!m_impl.m_modifications || !recv_no_log_write);
+  /* This is a dirty read, for debugging. */
+  ut_ad(!m_modifications || !recv_no_log_write);
+  ut_ad(!m_modifications || m_log_mode != MTR_LOG_NONE);
 
-	Command	cmd(this);
+  if (m_modifications
+      && (m_n_log_recs || m_log_mode == MTR_LOG_NO_REDO))
+  {
+    ut_ad(!srv_read_only_mode || m_log_mode == MTR_LOG_NO_REDO);
 
-	if (m_impl.m_modifications
-	    && (m_impl.m_n_log_recs > 0
-		|| m_impl.m_log_mode == MTR_LOG_NO_REDO)) {
+    lsn_t start_lsn;
 
-		ut_ad(!srv_read_only_mode
-		      || m_impl.m_log_mode == MTR_LOG_NO_REDO);
+    if (const ulint len= prepare_write())
+      start_lsn= finish_write(len);
+    else
+      start_lsn= m_commit_lsn;
 
-		cmd.execute();
-	} else {
-		cmd.release_all();
-		cmd.release_resources();
-	}
+    if (m_made_dirty)
+      log_flush_order_mutex_enter();
+
+    /* It is now safe to release the log mutex because the
+    flush_order mutex will ensure that we are the first one
+    to insert into the flush list. */
+    log_mutex_exit();
+
+    m_memo.for_each_block_in_reverse(CIterate<const ReleaseBlocks>
+                                     (ReleaseBlocks(start_lsn, m_commit_lsn,
+                                                    m_flush_observer)));
+    if (m_made_dirty)
+      log_flush_order_mutex_exit();
+
+    m_memo.for_each_block_in_reverse(CIterate<ReleaseLatches>());
+  }
+  else
+    m_memo.for_each_block_in_reverse(CIterate<ReleaseAll>());
+
+  release_resources();
 }
 
 /** Commit a mini-transaction that did not modify any pages,
@@ -580,37 +528,31 @@ mtr_t::commit_checkpoint(
 	ut_ad(log_mutex_own());
 	ut_ad(is_active());
 	ut_ad(!is_inside_ibuf());
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
 	ut_ad(get_log_mode() == MTR_LOG_ALL);
-	ut_ad(!m_impl.m_made_dirty);
-	ut_ad(m_impl.m_memo.size() == 0);
+	ut_ad(!m_made_dirty);
+	ut_ad(m_memo.size() == 0);
 	ut_ad(!srv_read_only_mode);
-	ut_d(m_impl.m_state = MTR_STATE_COMMITTING);
-	ut_ad(write_mlog_checkpoint || m_impl.m_n_log_recs > 1);
+	ut_ad(write_mlog_checkpoint || m_n_log_recs > 1);
 
-	switch (m_impl.m_n_log_recs) {
+	switch (m_n_log_recs) {
 	case 0:
 		break;
 	case 1:
-		*m_impl.m_log.front()->begin() |= MLOG_SINGLE_REC_FLAG;
+		*m_log.front()->begin() |= MLOG_SINGLE_REC_FLAG;
 		break;
 	default:
-		mlog_catenate_ulint(
-			&m_impl.m_log, MLOG_MULTI_REC_END, MLOG_1BYTE);
+		mlog_catenate_ulint(&m_log, MLOG_MULTI_REC_END, MLOG_1BYTE);
 	}
 
 	if (write_mlog_checkpoint) {
-		byte*	ptr = m_impl.m_log.push<byte*>(SIZE_OF_MLOG_CHECKPOINT);
-#if SIZE_OF_MLOG_CHECKPOINT != 9
-# error SIZE_OF_MLOG_CHECKPOINT != 9
-#endif
+		byte*	ptr = m_log.push<byte*>(SIZE_OF_MLOG_CHECKPOINT);
+		compile_time_assert(SIZE_OF_MLOG_CHECKPOINT == 1 + 8);
 		*ptr = MLOG_CHECKPOINT;
 		mach_write_to_8(ptr + 1, checkpoint_lsn);
 	}
 
-	Command	cmd(this);
-	cmd.finish_write(m_impl.m_log.size());
-	cmd.release_resources();
+	finish_write(m_log.size());
+	release_resources();
 
 	if (write_mlog_checkpoint) {
 		DBUG_PRINT("ib_log",
@@ -627,18 +569,12 @@ mtr_t::commit_checkpoint(
 bool
 mtr_t::is_named_space(ulint space) const
 {
-	ut_ad(!m_impl.m_sys_space
-	      || m_impl.m_sys_space->id == TRX_SYS_SPACE);
-	ut_ad(!m_impl.m_undo_space
-	      || m_impl.m_undo_space->id != TRX_SYS_SPACE);
-	ut_ad(!m_impl.m_user_space
-	      || m_impl.m_user_space->id != TRX_SYS_SPACE);
-	ut_ad(!m_impl.m_sys_space
-	      || m_impl.m_sys_space != m_impl.m_user_space);
-	ut_ad(!m_impl.m_sys_space
-	      || m_impl.m_sys_space != m_impl.m_undo_space);
-	ut_ad(!m_impl.m_user_space
-	      || m_impl.m_user_space != m_impl.m_undo_space);
+	ut_ad(!m_sys_space || m_sys_space->id == TRX_SYS_SPACE);
+	ut_ad(!m_undo_space || m_undo_space->id != TRX_SYS_SPACE);
+	ut_ad(!m_user_space || m_user_space->id != TRX_SYS_SPACE);
+	ut_ad(!m_sys_space || m_sys_space != m_user_space);
+	ut_ad(!m_sys_space || m_sys_space != m_undo_space);
+	ut_ad(!m_user_space || m_user_space != m_undo_space);
 
 	switch (get_log_mode()) {
 	case MTR_LOG_NONE:
@@ -646,7 +582,7 @@ mtr_t::is_named_space(ulint space) const
 		return(true);
 	case MTR_LOG_ALL:
 	case MTR_LOG_SHORT_INSERTS:
-		return(m_impl.m_user_space_id == space
+		return(m_user_space_id == space
 		       || is_predefined_tablespace(space));
 	}
 
@@ -666,17 +602,16 @@ mtr_t::x_lock_space(ulint space_id, const char* file, unsigned line)
 {
 	fil_space_t*	space;
 
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
 	ut_ad(is_active());
 
 	if (space_id == TRX_SYS_SPACE) {
-		space = m_impl.m_sys_space;
+		space = m_sys_space;
 
 		if (!space) {
-			space = m_impl.m_sys_space = fil_space_get(space_id);
+			space = m_sys_space = fil_space_get(space_id);
 		}
-	} else if ((space = m_impl.m_user_space) && space_id == space->id) {
-	} else if ((space = m_impl.m_undo_space) && space_id == space->id) {
+	} else if ((space = m_user_space) && space_id == space->id) {
+	} else if ((space = m_undo_space) && space_id == space->id) {
 	} else if (get_log_mode() == MTR_LOG_NO_REDO) {
 		space = fil_space_get(space_id);
 		ut_ad(space->purpose == FIL_TYPE_TEMPORARY
@@ -685,7 +620,7 @@ mtr_t::x_lock_space(ulint space_id, const char* file, unsigned line)
 		      || srv_is_tablespace_truncated(space->id));
 	} else {
 		/* called from trx_rseg_create() */
-		space = m_impl.m_undo_space = fil_space_get(space_id);
+		space = m_undo_space = fil_space_get(space_id);
 	}
 
 	ut_ad(space);
@@ -701,9 +636,9 @@ mtr_t::x_lock_space(ulint space_id, const char* file, unsigned line)
 void
 mtr_t::lookup_sys_space()
 {
-	ut_ad(!m_impl.m_sys_space);
-	m_impl.m_sys_space = fil_space_get(TRX_SYS_SPACE);
-	ut_ad(m_impl.m_sys_space);
+	ut_ad(!m_sys_space);
+	m_sys_space = fil_space_get(TRX_SYS_SPACE);
+	ut_ad(m_sys_space);
 }
 
 /** Look up the user tablespace.
@@ -712,10 +647,10 @@ void
 mtr_t::lookup_user_space(ulint space_id)
 {
 	ut_ad(space_id != TRX_SYS_SPACE);
-	ut_ad(m_impl.m_user_space_id == space_id);
-	ut_ad(!m_impl.m_user_space);
-	m_impl.m_user_space = fil_space_get(space_id);
-	ut_ad(m_impl.m_user_space);
+	ut_ad(m_user_space_id == space_id);
+	ut_ad(!m_user_space);
+	m_user_space = fil_space_get(space_id);
+	ut_ad(m_user_space);
 }
 
 /** Set the tablespace associated with the mini-transaction
@@ -724,14 +659,13 @@ mtr_t::lookup_user_space(ulint space_id)
 void
 mtr_t::set_named_space(fil_space_t* space)
 {
-	ut_ad(m_impl.m_user_space_id == TRX_SYS_SPACE);
-	ut_d(m_impl.m_user_space_id = space->id);
+	ut_ad(m_user_space_id == TRX_SYS_SPACE);
+	ut_d(m_user_space_id = space->id);
 	if (space->id == TRX_SYS_SPACE) {
-		ut_ad(m_impl.m_sys_space == NULL
-		      || m_impl.m_sys_space == space);
-		m_impl.m_sys_space = space;
+		ut_ad(!m_sys_space || m_sys_space == space);
+		m_sys_space = space;
 	} else {
-		m_impl.m_user_space = space;
+		m_user_space = space;
 	}
 }
 
@@ -740,16 +674,15 @@ mtr_t::set_named_space(fil_space_t* space)
 bool
 mtr_t::memo_release(const void* object, ulint type)
 {
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
 	ut_ad(is_active());
 
 	/* We cannot release a page that has been written to in the
 	middle of a mini-transaction. */
-	ut_ad(!m_impl.m_modifications || type != MTR_MEMO_PAGE_X_FIX);
+	ut_ad(!m_modifications || type != MTR_MEMO_PAGE_X_FIX);
 
 	Iterate<Find> iteration(Find(object, type));
 
-	if (!m_impl.m_memo.for_each_block_in_reverse(iteration)) {
+	if (!m_memo.for_each_block_in_reverse(iteration)) {
 		memo_slot_release(iteration.functor.m_slot);
 		return(true);
 	}
@@ -763,16 +696,15 @@ mtr_t::memo_release(const void* object, ulint type)
 void
 mtr_t::release_page(const void* ptr, mtr_memo_type_t type)
 {
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
 	ut_ad(is_active());
 
 	/* We cannot release a page that has been written to in the
 	middle of a mini-transaction. */
-	ut_ad(!m_impl.m_modifications || type != MTR_MEMO_PAGE_X_FIX);
+	ut_ad(!m_modifications || type != MTR_MEMO_PAGE_X_FIX);
 
 	Iterate<FindPage> iteration(FindPage(ptr, type));
 
-	if (!m_impl.m_memo.for_each_block_in_reverse(iteration)) {
+	if (!m_memo.for_each_block_in_reverse(iteration)) {
 		memo_slot_release(iteration.functor.get_slot());
 		return;
 	}
@@ -783,27 +715,20 @@ mtr_t::release_page(const void* ptr, mtr_memo_type_t type)
 
 /** Prepare to write the mini-transaction log to the redo log buffer.
 @return number of bytes to write in finish_write() */
-ulint
-mtr_t::Command::prepare_write()
+inline ulint mtr_t::prepare_write()
 {
 	ut_ad(!recv_no_log_write);
 
-	switch (m_impl->m_log_mode) {
-	case MTR_LOG_SHORT_INSERTS:
-		ut_ad(0);
-		/* fall through (write no redo log) */
-	case MTR_LOG_NO_REDO:
-	case MTR_LOG_NONE:
-		ut_ad(m_impl->m_log.size() == 0);
+	if (UNIV_UNLIKELY(m_log_mode != MTR_LOG_ALL)) {
+		ut_ad(m_log_mode == MTR_LOG_NO_REDO);
+		ut_ad(m_log.size() == 0);
 		log_mutex_enter();
-		m_end_lsn = m_start_lsn = log_sys->lsn;
-		return(0);
-	case MTR_LOG_ALL:
-		break;
+		m_commit_lsn = log_sys->lsn;
+		return 0;
 	}
 
-	ulint	len	= m_impl->m_log.size();
-	ulint	n_recs	= m_impl->m_n_log_recs;
+	ulint	len	= m_log.size();
+	ulint	n_recs	= m_n_log_recs;
 	ut_ad(len > 0);
 	ut_ad(n_recs > 0);
 
@@ -811,9 +736,9 @@ mtr_t::Command::prepare_write()
 		log_buffer_extend((len + 1) * 2);
 	}
 
-	ut_ad(m_impl->m_n_log_recs == n_recs);
+	ut_ad(m_n_log_recs == n_recs);
 
-	fil_space_t*	space = m_impl->m_user_space;
+	fil_space_t*	space = m_user_space;
 
 	if (space != NULL && is_predefined_tablespace(space->id)) {
 		/* Omit MLOG_FILE_NAME for predefined tablespaces. */
@@ -822,35 +747,32 @@ mtr_t::Command::prepare_write()
 
 	log_mutex_enter();
 
-	if (fil_names_write_if_was_clean(space, m_impl->m_mtr)) {
+	if (fil_names_write_if_was_clean(space, this)) {
 		/* This mini-transaction was the first one to modify
 		this tablespace since the latest checkpoint, so
 		some MLOG_FILE_NAME records were appended to m_log. */
-		ut_ad(m_impl->m_n_log_recs > n_recs);
-		mlog_catenate_ulint(
-			&m_impl->m_log, MLOG_MULTI_REC_END, MLOG_1BYTE);
-		len = m_impl->m_log.size();
+		ut_ad(m_n_log_recs > n_recs);
+		mlog_catenate_ulint(&m_log, MLOG_MULTI_REC_END, MLOG_1BYTE);
+		len = m_log.size();
 	} else {
 		/* This was not the first time of dirtying a
 		tablespace since the latest checkpoint. */
 
-		ut_ad(n_recs == m_impl->m_n_log_recs);
+		ut_ad(n_recs == m_n_log_recs);
 
 		if (n_recs <= 1) {
 			ut_ad(n_recs == 1);
 
 			/* Flag the single log record as the
 			only record in this mini-transaction. */
-			*m_impl->m_log.front()->begin()
-				|= MLOG_SINGLE_REC_FLAG;
+			*m_log.front()->begin() |= MLOG_SINGLE_REC_FLAG;
 		} else {
 			/* Because this mini-transaction comprises
 			multiple log records, append MLOG_MULTI_REC_END
 			at the end. */
 
-			mlog_catenate_ulint(
-				&m_impl->m_log, MLOG_MULTI_REC_END,
-				MLOG_1BYTE);
+			mlog_catenate_ulint(&m_log, MLOG_MULTI_REC_END,
+					    MLOG_1BYTE);
 			len++;
 		}
 	}
@@ -862,98 +784,37 @@ mtr_t::Command::prepare_write()
 }
 
 /** Append the redo log records to the redo log buffer
-@param[in] len	number of bytes to write */
-void
-mtr_t::Command::finish_write(
-	ulint	len)
+@param[in] len	number of bytes to write
+@return start_lsn */
+inline lsn_t mtr_t::finish_write(ulint len)
 {
-	ut_ad(m_impl->m_log_mode == MTR_LOG_ALL);
+	ut_ad(m_log_mode == MTR_LOG_ALL);
 	ut_ad(log_mutex_own());
-	ut_ad(m_impl->m_log.size() == len);
+	ut_ad(m_log.size() == len);
 	ut_ad(len > 0);
 
-	if (m_impl->m_log.is_small()) {
-		const mtr_buf_t::block_t*	front = m_impl->m_log.front();
+	lsn_t start_lsn;
+
+	if (m_log.is_small()) {
+		const mtr_buf_t::block_t* front = m_log.front();
 		ut_ad(len <= front->used());
 
-		m_end_lsn = log_reserve_and_write_fast(
-			front->begin(), len, &m_start_lsn);
+		m_commit_lsn = log_reserve_and_write_fast(front->begin(), len,
+							  &start_lsn);
 
-		if (m_end_lsn > 0) {
-			return;
+		if (m_commit_lsn) {
+			return start_lsn;
 		}
 	}
 
 	/* Open the database log for log_write_low */
-	m_start_lsn = log_reserve_and_open(len);
+	start_lsn = log_reserve_and_open(len);
 
 	mtr_write_log_t	write_log;
-	m_impl->m_log.for_each_block(write_log);
-
-	m_end_lsn = log_close();
-}
+	m_log.for_each_block(write_log);
 
-/** Release the latches and blocks acquired by this mini-transaction */
-void
-mtr_t::Command::release_all()
-{
-	m_impl->m_memo.for_each_block_in_reverse(CIterate<ReleaseAll>());
-
-	/* Note that we have released the latches. */
-	m_locks_released = 1;
-}
-
-/** Release the latches acquired by this mini-transaction */
-void
-mtr_t::Command::release_latches()
-{
-	m_impl->m_memo.for_each_block_in_reverse(CIterate<ReleaseLatches>());
-
-	/* Note that we have released the latches. */
-	m_locks_released = 1;
-}
-
-/** Release the blocks used in this mini-transaction */
-void
-mtr_t::Command::release_blocks()
-{
-	m_impl->m_memo.for_each_block_in_reverse(
-		CIterate<const ReleaseBlocks>(
-			ReleaseBlocks(m_start_lsn, m_end_lsn,
-				      m_impl->m_flush_observer)));
-}
-
-/** Write the redo log record, add dirty pages to the flush list and release
-the resources. */
-void
-mtr_t::Command::execute()
-{
-	ut_ad(m_impl->m_log_mode != MTR_LOG_NONE);
-
-	if (const ulint len = prepare_write()) {
-		finish_write(len);
-	}
-
-	if (m_impl->m_made_dirty) {
-		log_flush_order_mutex_enter();
-	}
-
-	/* It is now safe to release the log mutex because the
-	flush_order mutex will ensure that we are the first one
-	to insert into the flush list. */
-	log_mutex_exit();
-
-	m_impl->m_mtr->m_commit_lsn = m_end_lsn;
-
-	release_blocks();
-
-	if (m_impl->m_made_dirty) {
-		log_flush_order_mutex_exit();
-	}
-
-	release_latches();
-
-	release_resources();
+	m_commit_lsn = log_close();
+	return start_lsn;
 }
 
 /** Release the free extents that was reserved using
@@ -966,23 +827,22 @@ mtr_t::release_free_extents(ulint n_reserved)
 {
 	fil_space_t*	space;
 
-	ut_ad(m_impl.m_undo_space == NULL);
+	ut_ad(!m_undo_space);
 
-	if (m_impl.m_user_space != NULL) {
+	if (m_user_space) {
 
-		ut_ad(m_impl.m_user_space->id
-		      == m_impl.m_user_space_id);
-		ut_ad(memo_contains(get_memo(), &m_impl.m_user_space->latch,
+		ut_ad(m_user_space->id == m_user_space_id);
+		ut_ad(memo_contains(get_memo(), &m_user_space->latch,
 				    MTR_MEMO_X_LOCK));
 
-		space = m_impl.m_user_space;
+		space = m_user_space;
 	} else {
 
-		ut_ad(m_impl.m_sys_space->id == TRX_SYS_SPACE);
-		ut_ad(memo_contains(get_memo(), &m_impl.m_sys_space->latch,
+		ut_ad(m_sys_space->id == TRX_SYS_SPACE);
+		ut_ad(memo_contains(get_memo(), &m_sys_space->latch,
 				    MTR_MEMO_X_LOCK));
 
-		space = m_impl.m_sys_space;
+		space = m_sys_space;
 	}
 
 	space->release_free_extents(n_reserved);
@@ -1084,10 +944,9 @@ struct FlaggedCheck {
 bool
 mtr_t::memo_contains_flagged(const void* ptr, ulint flags) const
 {
-	ut_ad(m_impl.m_magic_n == MTR_MAGIC_N);
-	ut_ad(is_committing() || is_active());
+	ut_ad(is_active());
 
-	return !m_impl.m_memo.for_each_block_in_reverse(
+	return !m_memo.for_each_block_in_reverse(
 		CIterate<FlaggedCheck>(FlaggedCheck(ptr, flags)));
 }
 
@@ -1103,7 +962,7 @@ mtr_t::memo_contains_page_flagged(
 	ulint		flags) const
 {
 	Iterate<FindPage> iteration(FindPage(ptr, flags));
-	return m_impl.m_memo.for_each_block_in_reverse(iteration)
+	return m_memo.for_each_block_in_reverse(iteration)
 		? NULL : iteration.functor.get_block();
 }
 
@@ -1126,7 +985,7 @@ void
 mtr_t::print() const
 {
 	ib::info() << "Mini-transaction handle: memo size "
-		<< m_impl.m_memo.size() << " bytes log size "
+		<< m_memo.size() << " bytes log size "
 		<< get_log()->size() << " bytes";
 }