Add a more scalable ETS ordered_set implementation

The current ETS ordered_set implementation can quickly become a
scalability bottleneck on multicore machines when an application updates
an ordered_set table from concurrent processes [1][2]. The current
implementation is based on an AVL tree protected from concurrent writes
by a single readers-writer lock. Furthermore, the current implementation
has an optimization, called the stack optimization [3], that can improve
the performance when only a single process accesses a table but can
cause bad scalability even in read-only scenarios. It is possible to
pass the option {write_concurrency, true} to ets:new/2 when creating an
ETS table of type ordered_set but this option has no effect for tables
of type ordered_set without this commit. The new ETS ordered_set
implementation, added by this commit, is only activated when one passes
the options ordered_set and {write_concurrency, true} to the ets:new/2
function. Thus, the previous ordered_set implementation (from here on
called the default implementation) can still be used in applications
that do not benefit from the new implementation. The benchmark results
on the following web page show that the new implementation is many times
faster than the old implementation in some scenarios and that the old
implementation is still better than the new implementation in some
scenarios.

http://winsh.me/ets_catree_benchmark/ets_ca_tree_benchmark_results.html

The new implementation is expected to scale better than the default
implementation when concurrent processes use the following ETS
operations to operate on a table:

delete/2, delete_object/2, first/1, insert/2 (single object),
insert_new/2 (single object), lookup/2, lookup_element/2, member/2,
next/2, take/2 and update_element/3 (single object).

Currently, the new implementation does not have scalable support for the
other operations (e.g., select/2). However, when these operations are
used infrequently, the new implantation may still scale better than the
default implementation as the benchmark results at the URL above shows.

Description of the New Implementation
----------------------------------

The new implementation is based on a data structure which is called the
contention adapting search tree (CA tree for short). The following
publication contains a detailed description of the CA tree:

A Contention Adapting Approach to Concurrent Ordered Sets
Journal of Parallel and Distributed Computing, 2018
Kjell Winblad and Konstantinos Sagonas
https://doi.org/10.1016/j.jpdc.2017.11.007
http://www.it.uu.se/research/group/languages/software/ca_tree/catree_proofs.pdf

A discussion of how the CA tree can be used as an ETS back-end can be
found in another publication [1]. The CA tree is a data structure that
dynamically changes its synchronization granularity based on detected
contention. Internally, the CA tree uses instances of a sequential data
structure to store items. The CA tree implementation contained in this
commit uses the same AVL tree implementation as is used for the default
ordered set implementation. This AVL tree implementation is reused so
that much of the existing code to implement the ETS operations can be
reused.

Tests
-----

The ETS tests in `lib/stdlib/test/ets_SUITE.erl` have been extended to
also test the new ordered_set implementation. The function
ets_SUITE:throughput_benchmark/0 has also been added to this file. This
function can be used to measure and compare the performance of the
different ETS table types and options. This function writes benchmark
data to standard output that can be visualized by the HTML page
`lib/stdlib/test/ets_SUITE_data/visualize_throughput.html`.

[1]
More Scalable Ordered Set for ETS Using Adaptation.
In Thirteenth ACM SIGPLAN workshop on Erlang (2014).
Kjell Winblad and Konstantinos Sagonas.
https://doi.org/10.1145/2633448.2633455
http://www.it.uu.se/research/group/languages/software/ca_tree/erlang_paper.pdf

[2]
On the Scalability of the Erlang Term Storage
In Twelfth ACM SIGPLAN workshop on Erlang (2013)
Kjell Winblad, David Klaftenegger and Konstantinos Sagonas
https://doi.org/10.1145/2505305.2505308
http://winsh.me/papers/erlang_workshop_2013.pdf

[3]
The stack optimization works by keeping one preallocated stack instance
in every ordered_set table. This stack is updated so that it contains
the search path in some read operations (e.g., ets:next/2). This makes
it possible for a subsequent ets:next/2 to avoid traversing some nodes
in some cases. Unfortunately, the preallocated stack needs to be flagged
so that it is not updated concurrently by several threads which cause
bad scalability.

1 files changed, 91 insertions, 0 deletions

diff --git a/erts/emulator/beam/erl_db_catree.h b/erts/emulator/beam/erl_db_catree.h
new file mode 100644
index 0000000000..1f2c7da091
--- /dev/null
+++ b/erts/emulator/beam/erl_db_catree.h
@@ -0,0 +1,91 @@
+/*
+ * %CopyrightBegin%
+ *
+ * Copyright Ericsson AB 1998-2016. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * %CopyrightEnd%
+ */
+
+/*
+ * Description: Implementation of ETS ordered_set table type with
+ *              fine-grained synchronization.
+ *
+ * Author: 	Kjell Winblad
+ *
+ * "erl_db_catree.c" contains more details about the implementation.
+ *
+ */
+
+#ifndef _DB_CATREE_H
+#define _DB_CATREE_H
+
+struct DbTableCATreeNode;
+
+typedef struct {
+    erts_rwmtx_t lock; /* The lock for this base node */
+    Sint lock_statistics;
+    int is_valid; /* If this base node is still valid */
+    TreeDbTerm *root; /* The root of the sequential tree */
+    DbTable * tab; /* Table ptr, used when freeing using thread progress */
+    ErtsThrPrgrLaterOp free_item; /* Used when freeing using thread progress */
+    struct DbTableCATreeNode * next; /* Used when gradually deleting */
+} DbTableCATreeBaseNode;
+
+typedef struct {
+    ErtsThrPrgrLaterOp free_item; /* Used when freeing using thread progress */
+    DbTable* tab; /* Table ptr, used when freeing using thread progress */
+    erts_mtx_t lock; /* Used when joining route nodes */
+    int is_valid; /* If this route node is still valid */
+    erts_atomic_t left;
+    erts_atomic_t right;
+    DbTerm key;
+} DbTableCATreeRouteNode;
+
+typedef struct DbTableCATreeNode {
+    int is_base_node;
+    union {
+        DbTableCATreeRouteNode route;
+        DbTableCATreeBaseNode base;
+    } baseOrRoute;
+} DbTableCATreeNode;
+
+typedef struct {
+    Uint pos;          /* Current position on stack */
+    Uint size;         /* The size of the stack array */
+    DbTableCATreeNode** array; /* The stack */
+} CATreeNodeStack;
+
+typedef struct db_table_catree {
+    DbTableCommon common;
+
+    /* CA Tree-specific fields */
+    erts_atomic_t root;         /* The tree root (DbTableCATreeNode*) */
+    Uint deletion;		/* Being deleted */
+    DbTreeStack free_stack_elems;/* Used for deletion ...*/
+    CATreeNodeStack free_stack_rnodes;
+    DbTableCATreeNode *base_nodes_to_free_list;
+    int is_routing_nodes_freed;
+} DbTableCATree;
+
+void db_initialize_catree(void);
+
+int db_create_catree(Process *p, DbTable *tbl);
+
+
+#ifdef ERTS_ENABLE_LOCK_COUNT
+void erts_lcnt_enable_db_catree_lock_count(DbTableCATree *tb, int enable);
+#endif
+
+#endif /* _DB_CATREE_H */