Make a light weight version (default) of DEBUG HTSTATS (#12212)

The light version only shows the table sizes, while the pre-existing
version that shows chain length stats is reachable with the `full` argument.

This should allow looking into rehashing state, even on huge dicts, on
which we're afraid to run the command for fear of causing a server freeze.

Also, fix a possible overflow in dictGetStats.

src/debug.c

@@ -413,9 +413,9 @@ void debugCommand(client *c) {
 "    Create a memory leak of the input string.",
 "LOG <message>",
 "    Write <message> to the server log.",
-"HTSTATS <dbid>",
+"HTSTATS <dbid> [full]",
 "    Return hash table statistics of the specified Redis database.",
-"HTSTATS-KEY <key>",
+"HTSTATS-KEY <key> [full]",
 "    Like HTSTATS but for the hash table stored at <key>'s value.",
 "LOADAOF",
 "    Flush the AOF buffers on disk and reload the AOF in memory.",
@@ -883,10 +883,11 @@ NULL
         sizes = sdscatprintf(sizes,"sdshdr32:%d ",(int)sizeof(struct sdshdr32));
         sizes = sdscatprintf(sizes,"sdshdr64:%d ",(int)sizeof(struct sdshdr64));
         addReplyBulkSds(c,sizes);
-    } else if (!strcasecmp(c->argv[1]->ptr,"htstats") && c->argc == 3) {
+    } else if (!strcasecmp(c->argv[1]->ptr,"htstats") && c->argc >= 3) {
         long dbid;
         sds stats = sdsempty();
         char buf[4096];
+        int full = 0;
 
         if (getLongFromObjectOrReply(c, c->argv[2], &dbid, NULL) != C_OK) {
             sdsfree(stats);
@@ -897,20 +898,26 @@ NULL
             addReplyError(c,"Out of range database");
             return;
         }
+        if (c->argc >= 4 && !strcasecmp(c->argv[3]->ptr,"full"))
+            full = 1;
 
         stats = sdscatprintf(stats,"[Dictionary HT]\n");
-        dictGetStats(buf,sizeof(buf),server.db[dbid].dict);
+        dictGetStats(buf,sizeof(buf),server.db[dbid].dict,full);
         stats = sdscat(stats,buf);
 
         stats = sdscatprintf(stats,"[Expires HT]\n");
-        dictGetStats(buf,sizeof(buf),server.db[dbid].expires);
+        dictGetStats(buf,sizeof(buf),server.db[dbid].expires,full);
         stats = sdscat(stats,buf);
 
         addReplyVerbatim(c,stats,sdslen(stats),"txt");
         sdsfree(stats);
-    } else if (!strcasecmp(c->argv[1]->ptr,"htstats-key") && c->argc == 3) {
+    } else if (!strcasecmp(c->argv[1]->ptr,"htstats-key") && c->argc >= 3) {
         robj *o;
         dict *ht = NULL;
+        int full = 0;
+
+        if (c->argc >= 4 && !strcasecmp(c->argv[3]->ptr,"full"))
+            full = 1;
 
         if ((o = objectCommandLookupOrReply(c,c->argv[2],shared.nokeyerr))
                 == NULL) return;
@@ -933,7 +940,7 @@ NULL
                             "represented using an hash table");
         } else {
             char buf[4096];
-            dictGetStats(buf,sizeof(buf),ht);
+            dictGetStats(buf,sizeof(buf),ht,full);
             addReplyVerbatim(c,buf,strlen(buf),"txt");
         }
     } else if (!strcasecmp(c->argv[1]->ptr,"change-repl-id") && c->argc == 2) {

src/dict.c

@@ -1502,7 +1502,7 @@ dictEntry *dictFindEntryByPtrAndHash(dict *d, const void *oldptr, uint64_t hash)
 /* ------------------------------- Debugging ---------------------------------*/
 
 #define DICT_STATS_VECTLEN 50
-size_t _dictGetStatsHt(char *buf, size_t bufsize, dict *d, int htidx) {
+size_t _dictGetStatsHt(char *buf, size_t bufsize, dict *d, int htidx, int full) {
     unsigned long i, slots = 0, chainlen, maxchainlen = 0;
     unsigned long totchainlen = 0;
     unsigned long clvector[DICT_STATS_VECTLEN];
@@ -1513,6 +1513,20 @@ size_t _dictGetStatsHt(char *buf, size_t bufsize, dict *d, int htidx) {
             "No stats available for empty dictionaries\n");
     }
 
+    if (!full) {
+        l += snprintf(buf+l,bufsize-l,
+            "Hash table %d stats (%s):\n"
+            " table size: %lu\n"
+            " number of elements: %lu\n",
+            htidx, (htidx == 0) ? "main hash table" : "rehashing target",
+            DICTHT_SIZE(d->ht_size_exp[htidx]), d->ht_used[htidx]);
+
+        /* Make sure there is a NULL term at the end. */
+        buf[bufsize-1] = '\0';
+        /* Unlike snprintf(), return the number of characters actually written. */
+        return strlen(buf);
+    }
+
     /* Compute stats. */
     for (i = 0; i < DICT_STATS_VECTLEN; i++) clvector[i] = 0;
     for (i = 0; i < DICTHT_SIZE(d->ht_size_exp[htidx]); i++) {
@@ -1557,24 +1571,25 @@ size_t _dictGetStatsHt(char *buf, size_t bufsize, dict *d, int htidx) {
             i, clvector[i], ((float)clvector[i]/DICTHT_SIZE(d->ht_size_exp[htidx]))*100);
     }
 
+    /* Make sure there is a NULL term at the end. */
+    buf[bufsize-1] = '\0';
     /* Unlike snprintf(), return the number of characters actually written. */
-    if (bufsize) buf[bufsize-1] = '\0';
     return strlen(buf);
 }
 
-void dictGetStats(char *buf, size_t bufsize, dict *d) {
+void dictGetStats(char *buf, size_t bufsize, dict *d, int full) {
     size_t l;
     char *orig_buf = buf;
     size_t orig_bufsize = bufsize;
 
-    l = _dictGetStatsHt(buf,bufsize,d,0);
+    l = _dictGetStatsHt(buf,bufsize,d,0,full);
-    buf += l;
+    if (dictIsRehashing(d) && bufsize > l) {
-    bufsize -= l;
+        buf += l;
-    if (dictIsRehashing(d) && bufsize > 0) {
+        bufsize -= l;
-        _dictGetStatsHt(buf,bufsize,d,1);
+        _dictGetStatsHt(buf,bufsize,d,1,full);
     }
     /* Make sure there is a NULL term at the end. */
-    if (orig_bufsize) orig_buf[orig_bufsize-1] = '\0';
+    orig_buf[orig_bufsize-1] = '\0';
 }
 
 /* ------------------------------- Benchmark ---------------------------------*/

src/dict.h

@@ -210,7 +210,7 @@ void dictReleaseIterator(dictIterator *iter);
 dictEntry *dictGetRandomKey(dict *d);
 dictEntry *dictGetFairRandomKey(dict *d);
 unsigned int dictGetSomeKeys(dict *d, dictEntry **des, unsigned int count);
-void dictGetStats(char *buf, size_t bufsize, dict *d);
+void dictGetStats(char *buf, size_t bufsize, dict *d, int full);
 uint64_t dictGenHashFunction(const void *key, size_t len);
 uint64_t dictGenCaseHashFunction(const unsigned char *buf, size_t len);
 void dictEmpty(dict *d, void(callback)(dict*));