erts: Tweak hash shrink limit

* Only shrink when we can remove one segment and still remain
  below 50% table load.

* Only shrink down to two table segments. It just leads to a lot of
  potentially "unnecessary" rehashing to have a chance of getting rid
  of the last extra segment before the last delete op. I don't think
  it's worth it.

1 files changed, 2 insertions, 1 deletions

diff --git a/erts/emulator/beam/erl_db_hash.h b/erts/emulator/beam/erl_db_hash.h
index eae5537ba4..ecd2ca74a1 100644
--- a/erts/emulator/beam/erl_db_hash.h
+++ b/erts/emulator/beam/erl_db_hash.h
@@ -63,9 +63,10 @@ typedef struct db_table_hash_fine_locks {
 typedef struct db_table_hash {
     DbTableCommon common;
 
-    /* SMP: szm and nactive are write-protected by is_resizing or table write lock */
+    /* szm, nactive, shrink_limit are write-protected by is_resizing or table write lock */
     erts_atomic_t szm;     /* current size mask. */
     erts_atomic_t nactive; /* Number of "active" slots */
+    erts_atomic_t shrink_limit; /* Shrink table when fewer objects than this */
 
     erts_atomic_t segtab;  /* The segment table (struct segment**) */
     struct segment* first_segtab[1];