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, 13 insertions, 0 deletions

diff --git a/src/intset.c b/src/intset.c
index e96037da8..621a74283 100644
--- a/src/intset.c
+++ b/src/intset.c
@@ -265,6 +265,17 @@ int64_t intsetRandom(intset *is) {
     return _intsetGet(is,rand()%len);
 }
 
+/* Return the largest member. */
+int64_t intsetMax(intset *is) {
+    uint32_t len = intrev32ifbe(is->length);
+    return _intsetGet(is, len - 1);
+}
+
+/* Return the smallest member. */
+int64_t intsetMin(intset *is) {
+    return _intsetGet(is, 0);
+}
+
 /* Get the value at the given position. When this position is
  * out of range the function returns 0, when in range it returns 1. */
 uint8_t intsetGet(intset *is, uint32_t pos, int64_t *value) {
@@ -425,6 +436,8 @@ int intsetTest(int argc, char **argv, int flags) {
         is = intsetAdd(is,6,&success); assert(success);
         is = intsetAdd(is,4,&success); assert(success);
         is = intsetAdd(is,4,&success); assert(!success);
+        assert(6 == intsetMax(is));
+        assert(4 == intsetMin(is));
         ok();
         zfree(is);
     }