Optimize KEYS when pattern includes hashtag and implies a single slot. (#12754)

in #12536 we made a similar optimization for SCAN, now that hashtags in
patterns. When we can make sure all keys matching the pettern will be in
the same slot, we can limit the iteration to run only one one.

src/db.c

@@ -33,6 +33,7 @@
 #include "latency.h"
 #include "script.h"
 #include "functions.h"
+#include "cluster.h"
 
 #include <signal.h>
 #include <ctype.h>
@@ -993,13 +994,22 @@ void randomkeyCommand(client *c) {
 void keysCommand(client *c) {
     dictEntry *de;
     sds pattern = c->argv[1]->ptr;
-    int plen = sdslen(pattern), allkeys;
+    int plen = sdslen(pattern), allkeys, pslot = -1;
     long numkeys = 0;
     void *replylen = addReplyDeferredLen(c);
-    dbIterator *dbit = dbIteratorInit(c->db, DB_MAIN);
     allkeys = (pattern[0] == '*' && plen == 1);
+    if (!allkeys) {
+        pslot = patternHashSlot(pattern, plen);
+    }
+    dictIterator *di = NULL;
+    dbIterator *dbit = NULL;
+    if (server.cluster_enabled && !allkeys && pslot != -1) {
+        di = dictGetSafeIterator(c->db->dict[pslot]);
+    } else {
+        dbit = dbIteratorInit(c->db, DB_MAIN);
+    }
     robj keyobj;
-    while ((de = dbIteratorNext(dbit)) != NULL) {
+    while ((de = di ? dictNext(di) : dbIteratorNext(dbit)) != NULL) {
         sds key = dictGetKey(de);
 
         if (allkeys || stringmatchlen(pattern,plen,key,sdslen(key),0)) {
@@ -1012,7 +1022,10 @@ void keysCommand(client *c) {
         if (c->flags & CLIENT_CLOSE_ASAP)
             break;
     }
-    dbReleaseIterator(dbit);
+    if (di)
+        dictReleaseIterator(di);
+    if (dbit)
+        dbReleaseIterator(dbit);
     setDeferredArrayLen(c,replylen,numkeys);
 }
 

tests/unit/keyspace.tcl

@@ -34,6 +34,14 @@ start_server {tags {"keyspace"}} {
         r dbsize
     } {6}
 
+    test {KEYS with hashtag} {
+        foreach key {"{a}x" "{a}y" "{a}z" "{b}a" "{b}b" "{b}c"} {
+            r set $key hello
+        }
+        assert_equal [lsort [r keys "{a}*"]] [list "{a}x" "{a}y" "{a}z"]
+        assert_equal [lsort [r keys "*{b}*"]] [list "{b}a" "{b}b" "{b}c"]
+    } 
+
     test {DEL all keys} {
         foreach key [r keys *] {r del $key}
         r dbsize