ovsdb: generate update notifications for monitor_cond session

Hold session's conditions in ovsdb_monitor_session_condition. Pass it
to ovsdb_monitor for generating "update2" notifications.
Add functions that can generate "update2" notification for a
"monitor_cond" session.
JSON cache is enabled only for session's with true condition only.
"monitor_cond" and "monitor_cond_change" are RFC 7047 extensions
described by ovsdb-server(1) manpage.

Performance evaluation:
OVN is the main candidate for conditional monitoring usage. It is clear that
conditional monitoring reduces computation on the ovn-controller (client) side
due to the reduced size of flow tables and update messages. Performance
evaluation shows up to 75% computation reduction.
However, performance evaluation shows also a reduction in computation on the SB
ovsdb-server side proportional to the degree that each logical network is
spread over physical hosts in the DC. Evaluation shows that in a realistic
scenarios there is a computation reduction also in the server side.

Evaluation on simulated environment of 50 hosts and 1000 logical ports shows
the following results (cycles #):

LN spread over # hosts|    master    | patch        | change
-------------------------------------------------------------
            1         | 24597200127  | 24339235374  |  1.0%
            6         | 23788521572  | 19145229352  | 19.5%
           12         | 23886405758  | 17913143176  | 25.0%
           18         | 25812686279  | 23675094540  |  8.2%
           24         | 28414671499  | 24770202308  | 12.8%
           30         | 31487218890  | 28397543436  |  9.8%
           36         | 36116993930  | 34105388739  |  5.5%
           42         | 37898342465  | 38647139083  | -1.9%
           48         | 41637996229  | 41846616306  | -0.5%
           50         | 41679995357  | 43455565977  | -4.2%

Signed-off-by: Liran Schour <lirans@il.ibm.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

4 files changed, 444 insertions, 53 deletions

diff --git a/ovsdb/jsonrpc-server.c b/ovsdb/jsonrpc-server.c
index 3a69a8517..8fa4a1ee3 100644
--- a/ovsdb/jsonrpc-server.c
+++ b/ovsdb/jsonrpc-server.c
@@ -28,6 +28,7 @@
 #include "ovsdb-error.h"
 #include "ovsdb-parser.h"
 #include "ovsdb.h"
+#include "condition.h"
 #include "poll-loop.h"
 #include "reconnect.h"
 #include "row.h"
@@ -865,7 +866,8 @@ ovsdb_jsonrpc_session_got_request(struct ovsdb_jsonrpc_session *s,
             reply = execute_transaction(s, db, request);
         }
     } else if (!strcmp(request->method, "monitor") ||
-               (monitor2_enable__ && !strcmp(request->method, "monitor2"))) {
+               (monitor2_enable__ && !strcmp(request->method, "monitor2")) ||
+               !strcmp(request->method, "monitor_cond")) {
         struct ovsdb *db = ovsdb_jsonrpc_lookup_db(s, request, &reply);
         if (!reply) {
             int l = strlen(request->method) - strlen("monitor");
@@ -1064,6 +1066,7 @@ struct ovsdb_jsonrpc_monitor {
     uint64_t unflushed;         /* The first transaction that has not been
                                        flushed to the jsonrpc remote client. */
     enum ovsdb_monitor_version version;
+    struct ovsdb_monitor_session_condition *condition;/* Session's condition */
 };
 
 static struct ovsdb_jsonrpc_monitor *
@@ -1091,20 +1094,27 @@ parse_bool(struct ovsdb_parser *parser, const char *name, bool default_value)
 }
 
 static struct ovsdb_error * OVS_WARN_UNUSED_RESULT
-ovsdb_jsonrpc_parse_monitor_request(struct ovsdb_monitor *dbmon,
-                                    const struct ovsdb_table *table,
-                                    const struct json *monitor_request)
+ovsdb_jsonrpc_parse_monitor_request(
+                               struct ovsdb_monitor *dbmon,
+                               const struct ovsdb_table *table,
+                               struct ovsdb_monitor_session_condition *cond,
+                               const struct json *monitor_request)
 {
     const struct ovsdb_table_schema *ts = table->schema;
     enum ovsdb_monitor_selection select;
-    const struct json *columns, *select_json;
+    const struct json *columns, *select_json, *where = NULL;
     struct ovsdb_parser parser;
     struct ovsdb_error *error;
 
     ovsdb_parser_init(&parser, monitor_request, "table %s", ts->name);
+    if (cond) {
+        where = ovsdb_parser_member(&parser, "where", OP_ARRAY | OP_OPTIONAL);
+    }
     columns = ovsdb_parser_member(&parser, "columns", OP_ARRAY | OP_OPTIONAL);
+
     select_json = ovsdb_parser_member(&parser, "select",
                                       OP_OBJECT | OP_OPTIONAL);
+
     error = ovsdb_parser_finish(&parser);
     if (error) {
         return error;
@@ -1179,6 +1189,12 @@ ovsdb_jsonrpc_parse_monitor_request(struct ovsdb_monitor *dbmon,
             }
         }
     }
+    if (cond) {
+        error = ovsdb_monitor_table_condition_create(cond, table, where);
+        if (error) {
+            return error;
+        }
+    }
 
     return NULL;
 }
@@ -1217,6 +1233,9 @@ ovsdb_jsonrpc_monitor_create(struct ovsdb_jsonrpc_session *s, struct ovsdb *db,
     m->session = s;
     m->db = db;
     m->dbmon = ovsdb_monitor_create(db, m);
+    if (version == OVSDB_MONITOR_V2) {
+        m->condition = ovsdb_monitor_session_condition_create();
+    }
     m->unflushed = 0;
     m->version = version;
     hmap_insert(&s->monitors, &m->node, json_hash(monitor_id, 0));
@@ -1244,6 +1263,7 @@ ovsdb_jsonrpc_monitor_create(struct ovsdb_jsonrpc_session *s, struct ovsdb *db,
             for (i = 0; i < array->n; i++) {
                 error = ovsdb_jsonrpc_parse_monitor_request(m->dbmon,
                                                             table,
+                                                            m->condition,
                                                             array->elems[i]);
                 if (error) {
                     goto error;
@@ -1252,6 +1272,7 @@ ovsdb_jsonrpc_monitor_create(struct ovsdb_jsonrpc_session *s, struct ovsdb *db,
         } else {
             error = ovsdb_jsonrpc_parse_monitor_request(m->dbmon,
                                                         table,
+                                                        m->condition,
                                                         mr_value);
             if (error) {
                 goto error;
@@ -1267,6 +1288,11 @@ ovsdb_jsonrpc_monitor_create(struct ovsdb_jsonrpc_session *s, struct ovsdb *db,
         m->dbmon = dbmon;
     }
 
+    /* Only now we can bind session's condition to ovsdb_monitor */
+    if (m->condition) {
+        ovsdb_monitor_condition_bind(m->dbmon, m->condition);
+    }
+
     ovsdb_monitor_get_initial(m->dbmon);
     json = ovsdb_jsonrpc_monitor_compose_update(m, true);
     json = json ? json : json_object_create();
@@ -1323,7 +1349,7 @@ ovsdb_jsonrpc_monitor_compose_update(struct ovsdb_jsonrpc_monitor *m,
     }
 
     return ovsdb_monitor_get_update(m->dbmon, initial, &m->unflushed,
-                                    m->version);
+                                    m->condition, m->version);
 }
 
 static bool
@@ -1346,6 +1372,7 @@ ovsdb_jsonrpc_monitor_destroy(struct ovsdb_jsonrpc_monitor *m)
     json_destroy(m->monitor_id);
     hmap_remove(&m->session->monitors, &m->node);
     ovsdb_monitor_remove_jsonrpc_monitor(m->dbmon, m, m->unflushed);
+    ovsdb_monitor_session_condition_destroy(m->condition);
     free(m);
 }
 
diff --git a/ovsdb/monitor.c b/ovsdb/monitor.c
index 5228a0a77..b60ed6762 100644
--- a/ovsdb/monitor.c
+++ b/ovsdb/monitor.c
@@ -27,6 +27,7 @@
 #include "ovsdb-parser.h"
 #include "ovsdb.h"
 #include "row.h"
+#include "condition.h"
 #include "simap.h"
 #include "hash.h"
 #include "table.h"
@@ -37,10 +38,27 @@
 #include "monitor.h"
 #include "openvswitch/vlog.h"
 
+VLOG_DEFINE_THIS_MODULE(ovsdb_monitor);
 
 static const struct ovsdb_replica_class ovsdb_jsonrpc_replica_class;
 static struct hmap ovsdb_monitors = HMAP_INITIALIZER(&ovsdb_monitors);
 
+/* Keep state of session's conditions */
+struct ovsdb_monitor_session_condition {
+    bool conditional;
+    size_t n_true_cnd;
+    struct shash tables;     /* Contains
+                              *   "struct ovsdb_monitor_table_condition *"s. */
+};
+
+/* Monitored table session's conditions */
+struct ovsdb_monitor_table_condition {
+    const struct ovsdb_table *table;
+    struct ovsdb_monitor_table *mt;
+    struct ovsdb_condition old_condition;
+    struct ovsdb_condition new_condition;
+};
+
 /*  Backend monitor.
  *
  *  ovsdb_monitor keep track of the ovsdb changes.
@@ -129,9 +147,11 @@ struct ovsdb_monitor_table {
 };
 
 typedef struct json *
-(*compose_row_update_cb_func)(const struct ovsdb_monitor_table *mt,
-                              const struct ovsdb_monitor_row *row,
-                              bool initial, unsigned long int *changed);
+(*compose_row_update_cb_func)
+    (const struct ovsdb_monitor_table *mt,
+     const struct ovsdb_monitor_session_condition * condition,
+     const struct ovsdb_monitor_row *row,
+     bool initial, unsigned long int *changed);
 
 static void ovsdb_monitor_destroy(struct ovsdb_monitor *dbmon);
 static struct ovsdb_monitor_changes * ovsdb_monitor_table_add_changes(
@@ -421,6 +441,42 @@ ovsdb_monitor_add_column(struct ovsdb_monitor *dbmon,
     return NULL;
 }
 
+static void
+ovsdb_monitor_condition_add_columns(struct ovsdb_monitor *dbmon,
+                                    const struct ovsdb_table *table,
+                                    struct ovsdb_condition *condition)
+{
+    size_t n_columns;
+    int i;
+    const struct ovsdb_column **columns =
+        ovsdb_condition_get_columns(condition, &n_columns);
+
+    for (i = 0; i < n_columns; i++) {
+        ovsdb_monitor_add_column(dbmon, table, columns[i],
+                                 OJMS_NONE, false);
+    }
+
+    free(columns);
+}
+
+/* Bind this session's condition to ovsdb_monitor */
+void
+ovsdb_monitor_condition_bind(struct ovsdb_monitor *dbmon,
+                          struct ovsdb_monitor_session_condition *cond)
+{
+    struct shash_node *node;
+
+    SHASH_FOR_EACH(node, &cond->tables) {
+        struct ovsdb_monitor_table_condition *mtc = node->data;
+        struct ovsdb_monitor_table *mt =
+            shash_find_data(&dbmon->tables, mtc->table->schema->name);
+
+        mtc->mt = mt;
+        ovsdb_monitor_condition_add_columns(dbmon, mtc->table,
+                                            &mtc->new_condition);
+    }
+}
+
 static struct ovsdb_monitor_changes *
 ovsdb_monitor_table_add_changes(struct ovsdb_monitor_table *mt,
                                 uint64_t next_txn)
@@ -506,6 +562,161 @@ ovsdb_monitor_row_update_type(bool initial, const bool old, const bool new)
             : !new ? OJMS_DELETE
             : OJMS_MODIFY;
 }
+
+/* Set conditional monitoring mode only if we have non-empty condition in one
+ * of the tables at least */
+static inline void
+ovsdb_monitor_session_condition_set_mode(
+                                  struct ovsdb_monitor_session_condition *cond)
+{
+    cond->conditional = shash_count(&cond->tables) !=
+        cond->n_true_cnd;
+}
+
+/* Returnes an empty allocated session's condition state holder */
+struct ovsdb_monitor_session_condition *
+ovsdb_monitor_session_condition_create(void)
+{
+    struct ovsdb_monitor_session_condition *condition =
+        xzalloc(sizeof *condition);
+
+    condition->conditional = false;
+    shash_init(&condition->tables);
+    return condition;
+}
+
+void
+ovsdb_monitor_session_condition_destroy(
+                           struct ovsdb_monitor_session_condition *condition)
+{
+    struct shash_node *node, *next;
+
+    if (!condition) {
+        return;
+    }
+
+    SHASH_FOR_EACH_SAFE (node, next, &condition->tables) {
+        struct ovsdb_monitor_table_condition *mtc = node->data;
+
+        ovsdb_condition_destroy(&mtc->new_condition);
+        ovsdb_condition_destroy(&mtc->old_condition);
+        shash_delete(&condition->tables, node);
+        free(mtc);
+    }
+    free(condition);
+}
+
+struct ovsdb_error *
+ovsdb_monitor_table_condition_create(
+                         struct ovsdb_monitor_session_condition *condition,
+                         const struct ovsdb_table *table,
+                         const struct json *json_cnd)
+{
+    struct ovsdb_monitor_table_condition *mtc;
+    struct ovsdb_error *error;
+
+    mtc = xzalloc(sizeof *mtc);
+    mtc->table = table;
+    ovsdb_condition_init(&mtc->old_condition);
+    ovsdb_condition_init(&mtc->new_condition);
+
+    if (json_cnd) {
+        error = ovsdb_condition_from_json(table->schema,
+                                          json_cnd,
+                                          NULL,
+                                          &mtc->old_condition);
+        if (error) {
+            free(mtc);
+            return error;
+        }
+    }
+
+    shash_add(&condition->tables, table->schema->name, mtc);
+    /* On session startup old == new condition */
+    ovsdb_condition_clone(&mtc->new_condition, &mtc->old_condition);
+    if (ovsdb_condition_is_true(&mtc->old_condition)) {
+        condition->n_true_cnd++;
+        ovsdb_monitor_session_condition_set_mode(condition);
+    }
+
+    return NULL;
+}
+
+static bool
+ovsdb_monitor_get_table_conditions(
+                      const struct ovsdb_monitor_table *mt,
+                      const struct ovsdb_monitor_session_condition *condition,
+                      struct ovsdb_condition **old_condition,
+                      struct ovsdb_condition **new_condition)
+{
+    if (!condition) {
+        return false;
+    }
+
+    struct ovsdb_monitor_table_condition *mtc =
+        shash_find_data(&condition->tables, mt->table->schema->name);
+
+    if (!mtc) {
+        return false;
+    }
+    *old_condition = &mtc->old_condition;
+    *new_condition = &mtc->new_condition;
+
+    return true;
+}
+
+static enum ovsdb_monitor_selection
+ovsdb_monitor_row_update_type_condition(
+                      const struct ovsdb_monitor_table *mt,
+                      const struct ovsdb_monitor_session_condition *condition,
+                      bool initial,
+                      const struct ovsdb_datum *old,
+                      const struct ovsdb_datum *new)
+{
+    struct ovsdb_condition *old_condition, *new_condition;
+    enum ovsdb_monitor_selection type =
+        ovsdb_monitor_row_update_type(initial, old, new);
+
+    if (ovsdb_monitor_get_table_conditions(mt,
+                                           condition,
+                                           &old_condition,
+                                           &new_condition)) {
+        bool old_cond = !old ? false
+            : ovsdb_condition_empty_or_match_any(old,
+                                                 old_condition,
+                                                 mt->columns_index_map);
+        bool new_cond = !new ? false
+            : ovsdb_condition_empty_or_match_any(new,
+                                                 new_condition,
+                                                 mt->columns_index_map);
+
+        if (!old_cond && !new_cond) {
+            type = OJMS_NONE;
+        }
+
+        switch (type) {
+        case OJMS_INITIAL:
+        case OJMS_INSERT:
+            if (!new_cond) {
+                type = OJMS_NONE;
+            }
+            break;
+        case OJMS_MODIFY:
+            type = !old_cond ? OJMS_INSERT : !new_cond
+                ? OJMS_DELETE : OJMS_MODIFY;
+            break;
+        case OJMS_DELETE:
+            if (!old_cond) {
+                type = OJMS_NONE;
+            }
+            break;
+        case OJMS_NONE:
+            break;
+        }
+    }
+    return type;
+}
+
 static bool
 ovsdb_monitor_row_skip_update(const struct ovsdb_monitor_table *mt,
                               const struct ovsdb_monitor_row *row,
@@ -550,6 +761,7 @@ ovsdb_monitor_row_skip_update(const struct ovsdb_monitor_table *mt,
 static struct json *
 ovsdb_monitor_compose_row_update(
     const struct ovsdb_monitor_table *mt,
+    const struct ovsdb_monitor_session_condition *condition OVS_UNUSED,
     const struct ovsdb_monitor_row *row,
     bool initial, unsigned long int *changed)
 {
@@ -611,6 +823,7 @@ ovsdb_monitor_compose_row_update(
 static struct json *
 ovsdb_monitor_compose_row_update2(
     const struct ovsdb_monitor_table *mt,
+    const struct ovsdb_monitor_session_condition *condition,
     const struct ovsdb_monitor_row *row,
     bool initial, unsigned long int *changed)
 {
@@ -618,7 +831,8 @@ ovsdb_monitor_compose_row_update2(
     struct json *row_update2, *diff_json;
     size_t i;
 
-    type = ovsdb_monitor_row_update_type(initial, row->old, row->new);
+    type = ovsdb_monitor_row_update_type_condition(mt, condition, initial,
+                                                   row->old, row->new);
     if (ovsdb_monitor_row_skip_update(mt, row, type, changed)) {
         return NULL;
     }
@@ -688,9 +902,11 @@ ovsdb_monitor_max_columns(struct ovsdb_monitor *dbmon)
  * RFC 7047) for all the outstanding changes within 'monitor', starting from
  * 'transaction'.  */
 static struct json*
-ovsdb_monitor_compose_update(struct ovsdb_monitor *dbmon,
-                             bool initial, uint64_t transaction,
-                             compose_row_update_cb_func row_update)
+ovsdb_monitor_compose_update(
+                      struct ovsdb_monitor *dbmon,
+                      bool initial, uint64_t transaction,
+                      const struct ovsdb_monitor_session_condition *condition,
+                      compose_row_update_cb_func row_update)
 {
     struct shash_node *node;
     struct json *json;
@@ -712,7 +928,7 @@ ovsdb_monitor_compose_update(struct ovsdb_monitor *dbmon,
         HMAP_FOR_EACH_SAFE (row, next, hmap_node, &changes->rows) {
             struct json *row_json;
 
-            row_json = (*row_update)(mt, row, initial, changed);
+            row_json = (*row_update)(mt, condition, row, initial, changed);
             if (row_json) {
                 char uuid[UUID_LEN + 1];
 
@@ -746,11 +962,13 @@ ovsdb_monitor_compose_update(struct ovsdb_monitor *dbmon,
  * be used as part of the initial reply to a "monitor" request, false if it is
  * going to be used as part of an "update" notification. */
 struct json *
-ovsdb_monitor_get_update(struct ovsdb_monitor *dbmon,
-                         bool initial, uint64_t *unflushed_,
-                         enum ovsdb_monitor_version version)
+ovsdb_monitor_get_update(
+             struct ovsdb_monitor *dbmon,
+             bool initial, uint64_t *unflushed_,
+             const struct ovsdb_monitor_session_condition *condition,
+             enum ovsdb_monitor_version version)
 {
-    struct ovsdb_monitor_json_cache_node *cache_node;
+    struct ovsdb_monitor_json_cache_node *cache_node = NULL;
     struct shash_node *node;
     struct json *json;
     const uint64_t unflushed = *unflushed_;
@@ -758,19 +976,28 @@ ovsdb_monitor_get_update(struct ovsdb_monitor *dbmon,
 
     /* Return a clone of cached json if one exists. Otherwise,
      * generate a new one and add it to the cache.  */
-    cache_node = ovsdb_monitor_json_cache_search(dbmon, version, unflushed);
+    if (!condition || !condition->conditional) {
+        cache_node = ovsdb_monitor_json_cache_search(dbmon, version,
+                                                     unflushed);
+    }
     if (cache_node) {
         json = cache_node->json ? json_clone(cache_node->json) : NULL;
     } else {
         if (version == OVSDB_MONITOR_V1) {
-            json = ovsdb_monitor_compose_update(dbmon, initial, unflushed,
-                                        ovsdb_monitor_compose_row_update);
+            json =
+               ovsdb_monitor_compose_update(dbmon, initial, unflushed,
+                                            condition,
+                                            ovsdb_monitor_compose_row_update);
         } else {
             ovs_assert(version == OVSDB_MONITOR_V2);
-            json = ovsdb_monitor_compose_update(dbmon, initial, unflushed,
-                                        ovsdb_monitor_compose_row_update2);
+            json =
+               ovsdb_monitor_compose_update(dbmon, initial, unflushed,
+                                            condition,
+                                            ovsdb_monitor_compose_row_update2);
+        }
+        if (!condition || !condition->conditional) {
+            ovsdb_monitor_json_cache_insert(dbmon, version, unflushed, json);
         }
-        ovsdb_monitor_json_cache_insert(dbmon, version, unflushed, json);
     }
 
     /* Maintain transaction id of 'changes'. */
@@ -908,6 +1135,11 @@ ovsdb_monitor_changes_classify(enum ovsdb_monitor_selection type,
         return OVSDB_CHANGES_NO_EFFECT;
     }
 
+    if (type == OJMS_MODIFY) {
+        /* Condition might turn a modify operation to insert or delete */
+        type |= OJMS_INSERT | OJMS_DELETE;
+    }
+
     return (mt->select & type)
                 ?  OVSDB_CHANGES_REQUIRE_EXTERNAL_UPDATE
                 :  OVSDB_CHANGES_REQUIRE_INTERNAL_UPDATE;
@@ -935,19 +1167,18 @@ ovsdb_monitor_change_cb(const struct ovsdb_row *old,
     }
     mt = aux->mt;
 
-    HMAP_FOR_EACH(changes, hmap_node, &mt->changes) {
-        enum ovsdb_monitor_changes_efficacy efficacy;
-        enum ovsdb_monitor_selection type;
+    enum ovsdb_monitor_selection type =
+        ovsdb_monitor_row_update_type(false, old, new);
+    enum ovsdb_monitor_changes_efficacy efficacy =
+        ovsdb_monitor_changes_classify(type, mt, changed);
 
-        type = ovsdb_monitor_row_update_type(false, old, new);
-        efficacy = ovsdb_monitor_changes_classify(type, mt, changed);
+    HMAP_FOR_EACH(changes, hmap_node, &mt->changes) {
         if (efficacy > OVSDB_CHANGES_NO_EFFECT) {
             ovsdb_monitor_changes_update(old, new, mt, changes);
         }
-
-        if (aux->efficacy < efficacy) {
-            aux->efficacy = efficacy;
-        }
+    }
+    if (aux->efficacy < efficacy) {
+        aux->efficacy = efficacy;
     }
 
     return true;
diff --git a/ovsdb/monitor.h b/ovsdb/monitor.h
index 83dba0d71..a5495a431 100644
--- a/ovsdb/monitor.h
+++ b/ovsdb/monitor.h
@@ -19,8 +19,11 @@
 
 struct ovsdb_monitor;
 struct ovsdb_jsonrpc_monitor;
+struct ovsdb_monitor_session_condition;
+struct ovsdb_condition;
 
 enum ovsdb_monitor_selection {
+    OJMS_NONE = 0,              /* None for this iteration */
     OJMS_INITIAL = 1 << 0,      /* All rows when monitor is created. */
     OJMS_INSERT = 1 << 1,       /* New rows. */
     OJMS_DELETE = 1 << 2,       /* Deleted rows. */
@@ -58,10 +61,12 @@ const char * ovsdb_monitor_add_column(struct ovsdb_monitor *dbmon,
                               enum ovsdb_monitor_selection select,
                               bool monitored);
 
-struct json *ovsdb_monitor_get_update(struct ovsdb_monitor *dbmon,
-                                      bool initial,
-                                      uint64_t *unflushed_transaction,
-                                      enum ovsdb_monitor_version version);
+struct json *ovsdb_monitor_get_update(
+               struct ovsdb_monitor *dbmon,
+               bool initial,
+               uint64_t *unflushed_transaction,
+               const struct ovsdb_monitor_session_condition *condition,
+               enum ovsdb_monitor_version version);
 
 void ovsdb_monitor_table_add_select(struct ovsdb_monitor *dbmon,
                                     const struct ovsdb_table *table,
@@ -73,4 +78,21 @@ bool ovsdb_monitor_needs_flush(struct ovsdb_monitor *dbmon,
 void ovsdb_monitor_get_initial(const struct ovsdb_monitor *dbmon);
 
 void ovsdb_monitor_get_memory_usage(struct simap *usage);
+
+struct ovsdb_monitor_session_condition *
+ovsdb_monitor_session_condition_create(void);
+
+void
+ovsdb_monitor_session_condition_destroy(
+                          struct ovsdb_monitor_session_condition *condition);
+struct ovsdb_error *
+ovsdb_monitor_table_condition_create(
+                          struct ovsdb_monitor_session_condition *condition,
+                          const struct ovsdb_table *table,
+                          const struct json *json_cnd);
+
+void
+ovsdb_monitor_condition_bind(struct ovsdb_monitor *dbmon,
+                             struct ovsdb_monitor_session_condition *cond);
+
 #endif
diff --git a/ovsdb/ovsdb-server.1.in b/ovsdb/ovsdb-server.1.in
index f749af227..1d8fff78f 100644
--- a/ovsdb/ovsdb-server.1.in
+++ b/ovsdb/ovsdb-server.1.in
@@ -257,31 +257,141 @@ notifications (see below) to the request, it must be unique among all
 active monitors.  \fBovsdb\-server\fR rejects attempt to create two
 monitors with the same identifier.
 .
-.IP "4.1.12. Monitor2"
-A new monitor method added in Open vSwitch version 2.5. Monitor2 allows
-for more efficient update notifications (described below).
+.IP "4.1.12. Monitor_cond"
+A new monitor method added in Open vSwitch version 2.5. The monitor_cond
+request enables a client to replicate subsets of tables within an OVSDB
+database by requesting notifications of changes to rows matching one of
+the conditions specified in "where" by receiving the specified contents
+of these rows when table updates occur. Monitor_cond also allows a more
+efficient update notifications by receiving table-updates2 notifications
+(described below).
+.
 .IP
-The monitor method described in Section 4.1.5 also applies to
-monitor2, with the following exceptions.
+The monitor method described in Section 4.1.5 also applies to monitor_cond,
+with the following exceptions:
 .
 .RS
 .IP \(bu
-RPC request method becomes "monitor2".
+RPC request method becomes "monitor_cond".
 .IP \(bu
-Replay result follows <table-updates2>, described in Section 4.1.13.
+Reply result follows <table-updates2>, described in Section 4.1.14.
 .IP \(bu
 Subsequent changes are sent to the client using the "update2" monitor
-notification, described in Section 4.1.13
+notification, described in Section 4.1.14
+.IP \(bu
+Update notifications are being sent only for rows matching [<condition>*].
+.RE
+.
+.IP
+The request object has the following members:
+.
+.PP
+.RS
+.nf
+"method": "monitor_cond"
+"params": [<db-name>, <json-value>, <monitor-cond-requests>]
+"id": <nonnull-json-value>
+.fi
+.RE
+.
+.IP
+The <json-value> parameter is used to match subsequent update notifications
+(see below) to this request. The <monitor-cond-requests> object maps the name
+of the table to an array of <monitor-cond-request>.
+.
+.IP
+Each <monitor-cond-request> is an object with the following members:
+.
+.PP
+.RS
+.nf
+"columns": [<column>*]            optional
+"where": [<condition>*]           optional
+"select": <monitor-select>        optional
+.fi
+.RE
+.
+.IP
+The "columns", if present, define the columns within the table to be monitored
+that match conditions. If not present all columns are being monitored.
+.
+.IP
+The "where" if present is a JSON array of <condition> and boolean values. If not
+present or condition is an empty array, implicit True will be considered and
+updates on all rows will be sent.
+.
+.IP
+<monitor-select> is an object with the following members:
+.
+.PP
+.RS
+.nf
+"initial": <boolean>              optional
+"insert": <boolean>               optional
+"delete": <boolean>               optional
+"modify": <boolean>               optional
+.fi
+.RE
+.
+.IP
+The contents of this object specify how the columns or table are to be
+monitored as explained in more detail below.
+.
+.IP
+The response object has the following members:
+.
+.PP
+.RS
+.nf
+"result": <table-updates2>
+"error": null
+"id": same "id" as request
+.fi
+.RE
+.
+.IP
+The <table-updates2> object is described in detail in Section 4.1.14. It
+contains the contents of the tables for which "initial" rows are selected.
+If no tables initial contents are requested, then "result" is an empty object.
+.
+.IP
+Subsequently, when changes to a specified table that match one of the conditions
+in monitor-cond-request are committed, the changes are automatically sent to the
+client using the "update2" monitor notification (see Section 4.1.14). This
+monitoring persists until the JSON-RPC session terminates or until the client
+sends a "monitor_cancel" JSON-RPC request.
+.
+.IP
+Each <monitor-cond-request> specifies one or more conditions and the manner in
+which the rows that match the conditions are to be monitored. The circumstances in
+which an "update" notification is sent for a row within the table are determined by
+<monitor-select>:
+.
+.RS
+.IP \(bu
+If "initial" is omitted or true, every row in the original table that matches one of
+the conditions is sent as part of the response to the "monitor_cond" request.
+.IP \(bu
+If "insert" is omitted or true, "update" notifications are sent for rows newly
+inserted into the table that match conditions or for rows modified in the table
+so that their old version does not match the condition and new version does.
+.IP \(bu
+If "delete" is omitted or true, "update" notifications are sent for rows deleted
+from the table that match conditions or for rows modified in the table so that
+their old version does match the conditions and new version does not.
+.IP \(bu
+If "modify" is omitted or true, "update" notifications are sent whenever a row in
+the table that matches conditions in both old and new version is modified.
 .RE
 .
 .IP
-Both monitor and monitor2 sessions can exist concurrently. However,
-monitor and monitor2 shares the same <json-value> parameter space; it
-must be unique among all monitor and monitor2 sessions.
+Both monitor and monitor_cond sessions can exist concurrently. However,
+monitor and monitor_cond shares the same <json-value> parameter space; it
+must be unique among all monitor and monitor_cond sessions.
 .
-.IP "4.1.13. Update2 notification"
+.IP "4.1.14. Update2 notification"
 The "update2" notification is sent by the server to the client to report
-changes in tables that are being monitored following a "monitor2" request
+changes in tables that are being monitored following a "monitor_cond" request
 as described above. The notification has the following members:
 .
 .RS
@@ -296,7 +406,8 @@ as described above. The notification has the following members:
 The <json-value> in "params" is the same as the value passed as the
 <json-value>  in "params" for the corresponding "monitor" request.
 <table-updates2> is an object that maps from a table name to a <table-update2>.
-A <table-update2> is an object that maps from row's UUID to a <row-update2> object. A <row-update2> is an object with one of the following members:
+A <table-update2> is an object that maps from row's UUID to a <row-update2>
+object. A <row-update2> is an object with one of the following members:
 .
 .RS
 .IP "\(dqinitial\(dq: <row>"
@@ -338,8 +449,8 @@ elements, <row> includes the value from the new column.
 .
 .IP
 Initial views of rows are not presented in update2 notifications,
-but in the response object to the monitor2 request. The formatting of the
-<table-updates2> object, however, is the same in either case.
+but in the response object to the monitor_cond request. The formatting
+of the <table-updates2> object, however, is the same in either case.
 .
 .IP "5.1. Notation"
 For <condition>, RFC 7047 only allows the use of \fB!=\fR, \fB==\fR,