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doc/reference/reference_lua/box_stat/memtx.rst

@@ -14,85 +14,94 @@ box.stat.memtx()
 box.stat.memtx().tx
 -------------------
 
-* ``tx`` shows the statistics of the memtx transactional manager,
-  which is responsible for transactions (``box.stat.memtx().tx.txn``)
-  and multiversion concurrency control (``box.stat.memtx().tx.mvcc``).
-
-  * ``box.stat.memtx().tx.txn`` shows memory allocation related to transactions.
-
-    It consists of the following sections:
-
-    * ``statements`` are *transaction statements*.
-      As an example, consider a user starting a transaction with
-      ``space:replace{0, 1}`` within this transaction. Under the hood,
-      this operation becomes a statement for this transaction.
-    * ``user`` is the memory that a user allocated within
-      the current transaction using the Tarantool C API function
-      :ref:`box_txn_alloc() <txn-box_txn_alloc>`.
-    * ``system`` is the memory allocated for internal needs
-      (for example, logs) and savepoints.
-
-      For each section, Tarantool reports the following statistics:
-
-      * ``total`` is the number of bytes that are currently allocated in memtx
-        for all transactions within the section scope.
-      * ``avg`` is the average number of bytes that a single transaction uses
-        (equals ``total`` / number of open transactions).
-      * ``max`` is the maximal number of bytes that a single transaction uses.
-
-  * ``box.stat.memtx().tx.mvcc`` shows memory allocation related to
-    :ref:`multiversion concurrency control (MVCC) <txn_mode_transaction-manager>`.
-    MVCC is reponsible for isolating transactions.
-    It reveals conflicts and makes sure that tuples that do not belong to a particular
-    space but were (or could be) read by some transaction were not deleted.
-
-    It consists of the following sections:
-
-    * ``trackers`` is the memory allocated for *trackers* of transaction reads.
-      Like in the previous sections, Tarantool reports the total, average
-      and maximal number of bytes allocated for trackers per a single transaction.
-    * ``conflicts`` is the memory allocated for *conflicts*
-      which are entities created when transactional conflicts occur.
-      Like in the previous sections, Tarantool reports the total, average
-      and maximal number of allocated bytes.
-    * ``tuples`` is the memory allocated for storing tuples.
-      With MVCC, tuples are stored using the *stories* mechanism. Nearly every
-      tuple has its story. Even tuples in an index may have their stories, so
-      it may be useful to differentiate memory allocated for tuples and memory
-      allocated for stories.
-
-      All stored tuples fall into three categories, with memory statistics
-      reported for each category:
-
-      * ``tracking`` is for tuples that are not used by any transactions directly,
-        but MVCC uses them for tracking transaction reads.
-      * ``used`` is for tuples that are used by active read-write transactions.
-      * ``read_view`` is for tuples that are not used by active read-write transactions,
-        but are used by read-only transactions.
-
-        For each of the three categories, Tarantool reports two statistical blocks:
-
-        * ``stories`` is for stories.
-        * ``retained`` is for *retained* tuples which do not belong to any index,
-          but MVCC doesn't allow to delete them yet.
-
-        For each block, Tarantool reports the following statistics:
-
-        * ``count`` is the number of stories or retained tuples.
-        * ``total`` is the number of bytes allocated for stories or retained tuples.
+``tx`` shows the statistics of the memtx transactional manager,
+which is responsible for transactions (``box.stat.memtx().tx.txn``)
+and multiversion concurrency control (``box.stat.memtx().tx.mvcc``).
+
+* ``box.stat.memtx().tx.txn`` shows memory allocation related to transactions.
+
+   It consists of the following sections:
+
+  * ``statements`` are *transaction statements*.
+    As an example, consider a user starting a transaction with
+    ``space:replace{0, 1}`` within this transaction. Under the hood,
+    this operation becomes a statement for this transaction.
+  * ``user`` is the memory that a user allocated within
+    the current transaction using the Tarantool C API function
+    :ref:`box_txn_alloc() <txn-box_txn_alloc>`.
+  * ``system`` is the memory allocated for internal needs
+    (for example, logs) and savepoints.
+
+    .. _box_introspection-box_stat_memtx_tx_total_avg_max:
+
+    For each section, Tarantool reports the following statistics:
+
+    * ``total`` is the number of bytes that are currently allocated in memtx
+      for all transactions within the section scope.
+    * ``avg`` is the average number of bytes that a single transaction uses
+      (equals ``total`` / number of open transactions).
+    * ``max`` is the maximal number of bytes that a single transaction uses.
+
+* ``box.stat.memtx().tx.mvcc`` shows memory allocation related to
+  :ref:`multiversion concurrency control (MVCC) <txn_mode_transaction-manager>`.
+  MVCC is reponsible for isolating transactions.
+  It reveals conflicts and makes sure that tuples that do not belong to a particular
+  space but were (or could be) read by some transaction were not deleted.
+
+  It consists of the following sections:
+
+  * ``trackers`` is the memory allocated for *trackers* of transaction reads.
+    Like in the :ref:`previous sections <box_introspection-box_stat_memtx_tx_total_avg_max>`,
+    Tarantool reports the total, average, and maximal number of bytes allocated
+    for trackers per a single transaction.
+  * ``conflicts`` is the memory allocated for *conflicts*
+    which are entities created when transactional conflicts occur.
+    Like in the :ref:`previous sections <box_introspection-box_stat_memtx_tx_total_avg_max>`,
+    Tarantool reports the total, average, and maximal number of allocated bytes.
+  * ``tuples`` is the memory allocated for storing tuples.
+    With MVCC, tuples are stored using the *stories* mechanism. Nearly every
+    tuple has its story. Even tuples in an index may have their stories, so
+    it may be useful to differentiate memory allocated for tuples and memory
+    allocated for stories.
+
+    All stored tuples fall into three categories, with memory statistics
+    reported for each category:
+
+    * ``tracking`` is for tuples that are not used by any transactions directly,
+      but MVCC uses them for tracking transaction reads.
+    * ``used`` is for tuples that are used by active read-write transactions.
+      See a detailed :ref:`example <box_introspection-box_stat_memtx_tx_example>` below.
+    * ``read_view`` is for tuples that are not used by active read-write transactions,
+      but are used by read-only transactions.
+
+      For each of the three categories, Tarantool reports two statistical blocks:
+
+      * ``stories`` is for stories.
+      * ``retained`` is for *retained* tuples which do not belong to any index,
+        but MVCC doesn't allow to delete them yet.
+
+      For each block, Tarantool reports the following statistics:
+
+      * ``count`` is the number of stories or retained tuples.
+      * ``total`` is the number of bytes allocated for stories or retained tuples.
+
+.. _box_introspection-box_stat_memtx_tx_example:
 
 **Example**
 
-Let's get memory statistics for `used` tuples in a transaction.
+Let's get memory statistics for ``used`` tuples in a transaction.
 
-To make transactions work, we need to :ref:`enable the MVCC engine <txn_mode_mvcc-enabling>`.
-We'll do it within the first ``box.cfg{}`` call to a new Tarantool instance:
+First, we :ref:`enable MVCC <txn_mode_mvcc-enabling>` so that
+``box.stat.memtx.tx().mvcc`` contained non-zero values.
 
 .. code-block:: lua
 
    box.cfg{memtx_use_mvcc_engine = true}
 
-Next, we'll create a space with a primary index, and begin a transaction:
+We did it within the first ``box.cfg{}`` call to a new Tarantool instance,
+because the parameter ``memtx_use_mvcc_engine`` is non-dynamic.
+
+Next, we create a space with a primary index, and begin a transaction:
 
 .. code-block:: lua
 
@@ -112,8 +121,8 @@ In the transaction above, we replaced three tuples by the `0` key:
 * ``{0, 'aa...aa'}``
 * ``{0, 1}``
 
-MVCC considers all these tuples as `used` since they belong to the current transaction.
-Meanwhile, MVCC considers tuples ``{0, 0}`` and ``{0, 'aa..aa'}`` as `retained` because
+MVCC considers all these tuples as ``used`` since they belong to the current transaction.
+Also, MVCC considers tuples ``{0, 0}`` and ``{0, 'aa..aa'}`` as ``retained`` because
 they don't belong to any index (unlike ``{0, 1}``), but they cannot be deleted yet.
 
 If we call ``box.stat.memtx.tx()`` now, we'll see something like this:
@@ -169,10 +178,4 @@ If we call ``box.stat.memtx.tx()`` now, we'll see something like this:
 	          total: 0
 	...
 
-Pay attention to highlighted lines -- it's the memory used allocated for `used` tuples.
-
-For a neat experiment, let's commit the transaction:
-
-.. code-block:: lua
-
-   box.commit()
+Pay attention to highlighted lines -- it's the memory allocated for `used` tuples.

doc/reference/reference_lua/box_stat/reset.rst

@@ -7,6 +7,6 @@ box.stat.reset()
 
 .. function:: reset()
 
-    Resets the statistics of ``box.stat()``,
-    ``box.stat.net()``, ``box.stat.vinyl()``, and
+    Resets the statistics of ``box.stat()``, ``box.stat.net()``,
+    ``box.stat.memtx()``, ``box.stat.vinyl()``, and
     :ref:`box.space.index <box_space-space_index>`.