Introduce CLUSTER SLOT-STATS command (#20).

The command provides detailed slot usage statistics upon invocation,
with initial support for key-count metric. cpu-usec (approved) and
memory-bytes (pending-approval) metrics will soon follow after the
merger of this PR.

src/Makefile

@@ -383,7 +383,7 @@ endif
 ENGINE_NAME=valkey
 SERVER_NAME=$(ENGINE_NAME)-server$(PROG_SUFFIX)
 ENGINE_SENTINEL_NAME=$(ENGINE_NAME)-sentinel$(PROG_SUFFIX)
-ENGINE_SERVER_OBJ=threads_mngr.o adlist.o quicklist.o ae.o anet.o dict.o kvstore.o server.o sds.o zmalloc.o lzf_c.o lzf_d.o pqsort.o zipmap.o sha1.o ziplist.o release.o networking.o util.o object.o db.o replication.o rdb.o t_string.o t_list.o t_set.o t_zset.o t_hash.o config.o aof.o pubsub.o multi.o debug.o sort.o intset.o syncio.o cluster.o cluster_legacy.o crc16.o endianconv.o slowlog.o eval.o bio.o rio.o rand.o memtest.o syscheck.o crcspeed.o crc64.o bitops.o sentinel.o notify.o setproctitle.o blocked.o hyperloglog.o latency.o sparkline.o valkey-check-rdb.o valkey-check-aof.o geo.o lazyfree.o module.o evict.o expire.o geohash.o geohash_helper.o childinfo.o defrag.o siphash.o rax.o t_stream.o listpack.o localtime.o lolwut.o lolwut5.o lolwut6.o acl.o tracking.o socket.o tls.o sha256.o timeout.o setcpuaffinity.o monotonic.o mt19937-64.o resp_parser.o call_reply.o script_lua.o script.o functions.o function_lua.o commands.o strl.o connection.o unix.o logreqres.o
+ENGINE_SERVER_OBJ=threads_mngr.o adlist.o quicklist.o ae.o anet.o dict.o kvstore.o server.o sds.o zmalloc.o lzf_c.o lzf_d.o pqsort.o zipmap.o sha1.o ziplist.o release.o networking.o util.o object.o db.o replication.o rdb.o t_string.o t_list.o t_set.o t_zset.o t_hash.o config.o aof.o pubsub.o multi.o debug.o sort.o intset.o syncio.o cluster.o cluster_legacy.o cluster_slots.o crc16.o endianconv.o slowlog.o eval.o bio.o rio.o rand.o memtest.o syscheck.o crcspeed.o crc64.o bitops.o sentinel.o notify.o setproctitle.o blocked.o hyperloglog.o latency.o sparkline.o valkey-check-rdb.o valkey-check-aof.o geo.o lazyfree.o module.o evict.o expire.o geohash.o geohash_helper.o childinfo.o defrag.o siphash.o rax.o t_stream.o listpack.o localtime.o lolwut.o lolwut5.o lolwut6.o acl.o tracking.o socket.o tls.o sha256.o timeout.o setcpuaffinity.o monotonic.o mt19937-64.o resp_parser.o call_reply.o script_lua.o script.o functions.o function_lua.o commands.o strl.o connection.o unix.o logreqres.o
 ENGINE_CLI_NAME=$(ENGINE_NAME)-cli$(PROG_SUFFIX)
 ENGINE_CLI_OBJ=anet.o adlist.o dict.o valkey-cli.o zmalloc.o release.o ae.o serverassert.o crcspeed.o crc64.o siphash.o crc16.o monotonic.o cli_common.o mt19937-64.o strl.o cli_commands.o
 ENGINE_BENCHMARK_NAME=$(ENGINE_NAME)-benchmark$(PROG_SUFFIX)

src/cluster.h

@@ -103,6 +103,8 @@ char *clusterNodeHostname(clusterNode *node);
 const char *clusterNodePreferredEndpoint(clusterNode *n);
 long long clusterNodeReplOffset(clusterNode *node);
 clusterNode *clusterLookupNode(const char *name, int length);
+unsigned int countKeysInSlot(unsigned int hashslot);
+int getSlotOrReply(client *c, robj *o);
 
 /* functions with shared implementations */
 clusterNode *getNodeByQuery(client *c, struct serverCommand *cmd, robj **argv, int argc, int *hashslot, int *ask);

src/cluster_slots.c

@@ -0,0 +1,217 @@
+/* Cluster slots APIs and commands - to retrieve, update and process slot level data 
+ * in association with Valkey cluster.
+ *
+ * Copyright (c) 2024, Kyle Kim <kimkyle at amazon dot com>, Amazon Web Services.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Valkey nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "server.h"
+#include "cluster.h"
+#include "cluster_legacy.h"
+
+#define DEFAULT_SLOT -1
+#define DEFAULT_STAT 0
+#define UNASSIGNED_SLOT 0
+#define ORDER_BY_KEY_COUNT 1
+#define ORDER_BY_INVALID -1
+
+/* -----------------------------------------------------------------------------
+ * CLUSTER SLOT-STATS command
+ * -------------------------------------------------------------------------- */
+
+typedef struct sortedSlotStatEntry {
+    int slot;
+    uint64_t stat;
+} sortedSlotStatEntry;
+
+static int doesSlotBelongToMyShard(int slot) {
+    clusterNode *n = clusterNodeGetMaster(server.cluster->myself);
+    return server.cluster->slots[slot] == n;
+}
+
+static void markAssignedSlots(unsigned char *slots) {
+    for (int slot = 0; slot < CLUSTER_SLOTS; slot++) {
+        if (doesSlotBelongToMyShard(slot)) slots[slot]++;
+    }
+}
+
+static int countAssignedSlotsFromSlotsArray(unsigned char *slots) {
+    int count = 0;
+    for (int slot = 0; slot < CLUSTER_SLOTS; slot++) {
+        if (slots[slot]) count++;
+    }
+    return count;
+}
+
+static void checkSlotAssignment(unsigned char *slots, int start_slot, int end_slot) {
+    for (int slot = start_slot; slot <= end_slot; slot++) {
+        if (doesSlotBelongToMyShard(slot)) {
+            slots[slot]++;
+        }
+    }
+}
+
+static uint64_t getSingleSlotStat(int slot, int order_by) {
+    serverAssert(order_by != ORDER_BY_INVALID);
+    uint64_t singleSlotStat = 0;
+    if (order_by == ORDER_BY_KEY_COUNT) {
+        singleSlotStat = countKeysInSlot(slot);
+    }
+    return singleSlotStat;
+}
+
+static int slotStatEntryAscCmp(const void *a, const void *b) {
+    sortedSlotStatEntry entry_a = *((sortedSlotStatEntry *) a);
+    sortedSlotStatEntry entry_b = *((sortedSlotStatEntry *) b);
+    return entry_a.stat - entry_b.stat;
+}
+
+static int slotStatEntryDescCmp(const void *a, const void *b) {
+    sortedSlotStatEntry entry_a = *((sortedSlotStatEntry *) a);
+    sortedSlotStatEntry entry_b = *((sortedSlotStatEntry *) b);
+    return entry_b.stat - entry_a.stat;
+}
+
+static void sortSlotStats(sortedSlotStatEntry sorted[], int order_by, int desc) {
+    int i = 0;
+
+    for (int slot = 0; slot < CLUSTER_SLOTS; slot++) {
+        if (doesSlotBelongToMyShard(slot)) {
+            sorted[i].slot = slot;
+            sorted[i].stat = getSingleSlotStat(slot, order_by);
+            i++;
+        }
+    }
+    qsort(sorted, i, sizeof(sortedSlotStatEntry), (desc) ? slotStatEntryDescCmp : slotStatEntryAscCmp);
+}
+
+static void addReplySingleSlotStat(client *c, int slot) {
+    addReplyLongLong(c, slot);
+    addReplyMapLen(c, 1);
+    addReplyBulkCString(c, "key-count");
+    addReplyLongLong(c, countKeysInSlot(slot));
+}
+
+static void addReplySlotStats(client *c, unsigned char *slots) {
+    int num_slots_assigned = countAssignedSlotsFromSlotsArray(slots);
+    addReplyMapLen(c, num_slots_assigned);
+
+    for (int slot = 0; slot < CLUSTER_SLOTS; slot++) {
+        if (slots[slot]) addReplySingleSlotStat(c, slot);
+    }
+}
+
+static void addReplySortedSlotStats(client *c, sortedSlotStatEntry sorted[], long limit) {
+    int num_slots_assigned = getMyShardSlotCount();
+    int len = min(limit, num_slots_assigned);
+    addReplyMapLen(c, len);
+
+    for (int i = 0; i < len; i++) {
+        addReplySingleSlotStat(c, sorted[i].slot);
+    }
+}
+
+static void sortAndAddReplySlotStats(client *c, int order_by, long limit, int desc) {
+    sortedSlotStatEntry sorted[CLUSTER_SLOTS];
+    sortSlotStats(sorted, order_by, desc);
+    addReplySortedSlotStats(c, sorted, limit);
+}
+
+void clusterSlotStatsCommand(client *c) {
+    if (server.cluster_enabled == 0) {
+        addReplyError(c,"This instance has cluster support disabled");
+        return;
+    }
+
+    /* Initialize slot assignment array. */
+    unsigned char slots[CLUSTER_SLOTS]= {UNASSIGNED_SLOT};
+
+    /* No further arguments. */
+    if (c->argc == 2) {
+        /* CLUSTER SLOT-STATS */
+        markAssignedSlots(slots);
+        addReplySlotStats(c, slots);
+        return;
+    }
+
+    /* Parse additional arguments. */
+    if (!strcasecmp(c->argv[2]->ptr,"slotsrange") && c->argc == 5) {
+        /* CLUSTER SLOT-STATS SLOTSRANGE start-slot end-slot */
+        int startslot, endslot;
+        if ((startslot = getSlotOrReply(c,c->argv[3])) == C_ERR ||
+            (endslot = getSlotOrReply(c,c->argv[4])) == C_ERR) {
+            return;
+        }
+        if (startslot > endslot) {
+            addReplyErrorFormat(c,"start slot number %d is greater than end slot number %d", startslot, endslot);
+            return;
+        }
+        checkSlotAssignment(slots, startslot, endslot);
+        addReplySlotStats(c, slots);
+    } else if (!strcasecmp(c->argv[2]->ptr,"orderby") && c->argc >= 4) {
+        /* CLUSTER SLOT-STATS ORDERBY column [LIMIT limit] [ASC | DESC] */
+        int desc = 1, order_by = ORDER_BY_INVALID;
+        if (!strcasecmp(c->argv[3]->ptr, "key-count")) {
+            order_by = ORDER_BY_KEY_COUNT;
+        } else {
+            addReplyError(c, "unrecognized sort column for ORDER BY. The supported columns are: key-count.");
+            return;
+        }
+        int i = 4; /* Next argument index, following ORDERBY */
+        int limit_counter = 0, asc_desc_counter = 0;
+        long limit;
+        while(i < c->argc) {
+            int moreargs = c->argc > i+1;
+            if (!strcasecmp(c->argv[i]->ptr,"limit") && moreargs) {
+                if (getRangeLongFromObjectOrReply(
+                    c, c->argv[i+1], 1, CLUSTER_SLOTS, &limit,
+                    "limit has to lie in between 1 and 16384 (maximum number of slots)") != C_OK)
+                    return;
+                i++;
+                limit_counter++;
+            } else if (!strcasecmp(c->argv[i]->ptr,"asc")) {
+                desc = 0;
+                asc_desc_counter++;
+            } else if (!strcasecmp(c->argv[i]->ptr,"desc")) {
+                desc = 1;
+                asc_desc_counter++;
+            } else {
+                addReplyErrorObject(c,shared.syntaxerr);
+                return;
+            }
+
+            if (limit_counter > 1 || asc_desc_counter > 1) {
+                addReplyError(c, "you cannot provide multiple filters of the same type.");
+                return;
+            }
+            i++;
+        }
+        sortAndAddReplySlotStats(c, order_by, limit, desc);
+    } else {
+        addReplySubcommandSyntaxError(c);
+    }
+}

src/commands.def

@@ -921,6 +921,56 @@ struct COMMAND_ARG CLUSTER_SLAVES_Args[] = {
 {MAKE_ARG("node-id",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_NONE,0,NULL)},
 };
 
+/********** CLUSTER SLOT_STATS ********************/
+
+#ifndef SKIP_CMD_HISTORY_TABLE
+/* CLUSTER SLOT_STATS history */
+#define CLUSTER_SLOT_STATS_History NULL
+#endif
+
+#ifndef SKIP_CMD_TIPS_TABLE
+/* CLUSTER SLOT_STATS tips */
+const char *CLUSTER_SLOT_STATS_Tips[] = {
+"nondeterministic_output",
+"all_shards",
+};
+#endif
+
+#ifndef SKIP_CMD_KEY_SPECS_TABLE
+/* CLUSTER SLOT_STATS key specs */
+#define CLUSTER_SLOT_STATS_Keyspecs NULL
+#endif
+
+/* CLUSTER SLOT_STATS filter slotsrange argument table */
+struct COMMAND_ARG CLUSTER_SLOT_STATS_filter_slotsrange_Subargs[] = {
+{MAKE_ARG("start-slot",ARG_TYPE_INTEGER,-1,NULL,NULL,NULL,CMD_ARG_NONE,0,NULL)},
+{MAKE_ARG("end-slot",ARG_TYPE_INTEGER,-1,NULL,NULL,NULL,CMD_ARG_NONE,0,NULL)},
+};
+
+/* CLUSTER SLOT_STATS filter orderby order argument table */
+struct COMMAND_ARG CLUSTER_SLOT_STATS_filter_orderby_order_Subargs[] = {
+{MAKE_ARG("asc",ARG_TYPE_PURE_TOKEN,-1,"ASC",NULL,NULL,CMD_ARG_NONE,0,NULL)},
+{MAKE_ARG("desc",ARG_TYPE_PURE_TOKEN,-1,"DESC",NULL,NULL,CMD_ARG_NONE,0,NULL)},
+};
+
+/* CLUSTER SLOT_STATS filter orderby argument table */
+struct COMMAND_ARG CLUSTER_SLOT_STATS_filter_orderby_Subargs[] = {
+{MAKE_ARG("column",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_NONE,0,NULL)},
+{MAKE_ARG("limit",ARG_TYPE_INTEGER,-1,"LIMIT",NULL,NULL,CMD_ARG_OPTIONAL,0,NULL)},
+{MAKE_ARG("order",ARG_TYPE_ONEOF,-1,NULL,NULL,NULL,CMD_ARG_OPTIONAL,2,NULL),.subargs=CLUSTER_SLOT_STATS_filter_orderby_order_Subargs},
+};
+
+/* CLUSTER SLOT_STATS filter argument table */
+struct COMMAND_ARG CLUSTER_SLOT_STATS_filter_Subargs[] = {
+{MAKE_ARG("slotsrange",ARG_TYPE_BLOCK,-1,"SLOTSRANGE",NULL,NULL,CMD_ARG_OPTIONAL,2,NULL),.subargs=CLUSTER_SLOT_STATS_filter_slotsrange_Subargs},
+{MAKE_ARG("orderby",ARG_TYPE_BLOCK,-1,"ORDERBY",NULL,NULL,CMD_ARG_OPTIONAL,3,NULL),.subargs=CLUSTER_SLOT_STATS_filter_orderby_Subargs},
+};
+
+/* CLUSTER SLOT_STATS argument table */
+struct COMMAND_ARG CLUSTER_SLOT_STATS_Args[] = {
+{MAKE_ARG("filter",ARG_TYPE_ONEOF,-1,NULL,NULL,NULL,CMD_ARG_OPTIONAL,2,NULL),.subargs=CLUSTER_SLOT_STATS_filter_Subargs},
+};
+
 /********** CLUSTER SLOTS ********************/
 
 #ifndef SKIP_CMD_HISTORY_TABLE
@@ -972,6 +1022,7 @@ struct COMMAND_STRUCT CLUSTER_Subcommands[] = {
 {MAKE_CMD("setslot","Binds a hash slot to a node.","O(1)","3.0.0",CMD_DOC_NONE,NULL,NULL,"cluster",COMMAND_GROUP_CLUSTER,CLUSTER_SETSLOT_History,0,CLUSTER_SETSLOT_Tips,0,clusterCommand,-4,CMD_NO_ASYNC_LOADING|CMD_ADMIN|CMD_STALE,0,CLUSTER_SETSLOT_Keyspecs,0,NULL,2),.args=CLUSTER_SETSLOT_Args},
 {MAKE_CMD("shards","Returns the mapping of cluster slots to shards.","O(N) where N is the total number of cluster nodes","7.0.0",CMD_DOC_NONE,NULL,NULL,"cluster",COMMAND_GROUP_CLUSTER,CLUSTER_SHARDS_History,0,CLUSTER_SHARDS_Tips,1,clusterCommand,2,CMD_LOADING|CMD_STALE,0,CLUSTER_SHARDS_Keyspecs,0,NULL,0)},
 {MAKE_CMD("slaves","Lists the replica nodes of a master node.","O(N) where N is the number of replicas.","3.0.0",CMD_DOC_DEPRECATED,"`CLUSTER REPLICAS`","5.0.0","cluster",COMMAND_GROUP_CLUSTER,CLUSTER_SLAVES_History,0,CLUSTER_SLAVES_Tips,1,clusterCommand,3,CMD_ADMIN|CMD_STALE,0,CLUSTER_SLAVES_Keyspecs,0,NULL,1),.args=CLUSTER_SLAVES_Args},
+{MAKE_CMD("slot-stats","Return array of slot usage statistics for slots assigned to the current node","O(N) where N is the total number of slots based on arguments. O(N log N) with ORDERBY subcommand.","7.2.6",CMD_DOC_NONE,NULL,NULL,"cluster",COMMAND_GROUP_CLUSTER,CLUSTER_SLOT_STATS_History,0,CLUSTER_SLOT_STATS_Tips,2,clusterSlotStatsCommand,-2,CMD_STALE|CMD_LOADING,0,CLUSTER_SLOT_STATS_Keyspecs,0,NULL,1),.args=CLUSTER_SLOT_STATS_Args},
 {MAKE_CMD("slots","Returns the mapping of cluster slots to nodes.","O(N) where N is the total number of Cluster nodes","3.0.0",CMD_DOC_DEPRECATED,"`CLUSTER SHARDS`","7.0.0","cluster",COMMAND_GROUP_CLUSTER,CLUSTER_SLOTS_History,2,CLUSTER_SLOTS_Tips,1,clusterCommand,2,CMD_LOADING|CMD_STALE,0,CLUSTER_SLOTS_Keyspecs,0,NULL,0)},
 {0}
 };

src/commands/cluster-slot-stats.json

@@ -0,0 +1,79 @@
+{
+    "SLOT-STATS": {
+        "summary": "Return array of slot usage statistics for slots assigned to the current node",
+        "complexity": "O(N) where N is the total number of slots based on arguments. O(N log N) with ORDERBY subcommand.",
+        "group": "cluster",
+        "since": "7.2.6",
+        "arity": -2,
+        "container": "CLUSTER",
+        "function": "clusterSlotStatsCommand",
+        "command_flags": [
+            "STALE",
+            "LOADING"
+        ],
+        "command_tips": [
+            "NONDETERMINISTIC_OUTPUT",
+            "ALL_SHARDS"
+        ],
+        "arguments": [
+            {
+                "name": "filter",
+                "type": "oneof",
+                "optional": true,
+                "arguments": [
+                    {
+                        "token": "SLOTSRANGE",
+                        "name": "slotsrange",
+                        "type": "block",
+                        "optional": true,
+                        "arguments": [
+                            {
+                                "name": "start-slot",
+                                "type": "integer"
+                            },
+                            {
+                                "name": "end-slot",
+                                "type": "integer"
+                            }
+                        ]
+                    },
+                    {
+                        "token": "ORDERBY",
+                        "name": "orderby",
+                        "type": "block",
+                        "optional": true,
+                        "arguments": [
+                            {
+                                "name": "column",
+                                "type": "string"
+                            },
+                            {
+                                "token": "LIMIT",
+                                "name": "limit",
+                                "type": "integer",
+                                "optional": true
+                            },
+                            {
+                                "name": "order",
+                                "type": "oneof",
+                                "optional": true,
+                                "arguments": [
+                                    {
+                                        "name": "asc",
+                                        "type": "pure-token",
+                                        "token": "ASC"
+                                    },
+                                    {
+                                        "name": "desc",
+                                        "type": "pure-token",
+                                        "token": "DESC"
+                                    }
+                                ]
+                            }
+                        ]
+                    }
+                ]
+            }
+        ]
+    }
+}

src/server.h

@@ -3662,6 +3662,7 @@ void sunsubscribeCommand(client *c);
 void watchCommand(client *c);
 void unwatchCommand(client *c);
 void clusterCommand(client *c);
+void clusterSlotStatsCommand(client *c);
 void restoreCommand(client *c);
 void migrateCommand(client *c);
 void askingCommand(client *c);