Listpack encoding for sets (#11290)

Small sets with not only integer elements are listpack encoded, by default
up to 128 elements, max 64 bytes per element, new config `set-max-listpack-entries`
and `set-max-listpack-value`. This saves memory for small sets compared to using a hashtable.

Sets with only integers, even very small sets, are still intset encoded (up to 1G
limit, etc.). Larger sets are hashtable encoded.

This PR increments the RDB version, and has an effect on OBJECT ENCODING

Possible conversions when elements are added:

    intset -> listpack
    listpack -> hashtable
    intset -> hashtable

Note: No conversion happens when elements are deleted. If all elements are
deleted and then added again, the set is deleted and recreated, thus implicitly
converted to a smaller encoding.

1 files changed, 6 insertions, 4 deletions

diff --git a/src/defrag.c b/src/defrag.c
index ced4fd20a..e78c07929 100644
--- a/src/defrag.c
+++ b/src/defrag.c
@@ -874,10 +874,12 @@ long defragKey(redisDb *db, dictEntry *de) {
     } else if (ob->type == OBJ_SET) {
         if (ob->encoding == OBJ_ENCODING_HT) {
             defragged += defragSet(db, de);
-        } else if (ob->encoding == OBJ_ENCODING_INTSET) {
-            intset *newis, *is = ob->ptr;
-            if ((newis = activeDefragAlloc(is)))
-                defragged++, ob->ptr = newis;
+        } else if (ob->encoding == OBJ_ENCODING_INTSET ||
+                   ob->encoding == OBJ_ENCODING_LISTPACK)
+        {
+            void *newptr, *ptr = ob->ptr;
+            if ((newptr = activeDefragAlloc(ptr)))
+                defragged++, ob->ptr = newptr;
         } else {
             serverPanic("Unknown set encoding");
         }