From 687850a612465cee9b484670b1f4b6c15fb5a6fe Mon Sep 17 00:00:00 2001
From: John Sully <john@csquare.ca>
Date: Mon, 24 Oct 2022 15:27:10 +0000
Subject: [PATCH] Make semi-ordered-set rehashing configurable to aid in
 latency tuning

---
 src/config.cpp       | 2 ++
 src/semiorderedset.h | 8 ++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/config.cpp b/src/config.cpp
index 253f0726a..bb2a1f413 100644
--- a/src/config.cpp
+++ b/src/config.cpp
@@ -40,6 +40,7 @@
 #endif
 
 const char *KEYDB_SET_VERSION = KEYDB_REAL_VERSION;
+size_t g_semiOrderedSetTargetBucketSize = 0;    // Its a header only class so nowhere else for this to go
 
 /*-----------------------------------------------------------------------------
  * Config file name-value maps.
@@ -2910,6 +2911,7 @@ standardConfig configs[] = {
     createBoolConfig("allow-write-during-load", NULL, MODIFIABLE_CONFIG, g_pserver->fWriteDuringActiveLoad, 0, NULL, NULL),
     createBoolConfig("force-backlog-disk-reserve", NULL, MODIFIABLE_CONFIG, cserver.force_backlog_disk, 0, NULL, NULL),
     createBoolConfig("soft-shutdown", NULL, MODIFIABLE_CONFIG, g_pserver->config_soft_shutdown, 0, NULL, NULL),
+    createSizeTConfig("semi-ordered-set-bucket-size", NULL, MODIFIABLE_CONFIG, 0, 1024, g_semiOrderedSetTargetBucketSize, 0, INTEGER_CONFIG, NULL, NULL),
 
 #ifdef USE_OPENSSL
     createIntConfig("tls-port", NULL, MODIFIABLE_CONFIG, 0, 65535, g_pserver->tls_port, 0, INTEGER_CONFIG, NULL, updateTLSPort), /* TCP port. */
diff --git a/src/semiorderedset.h b/src/semiorderedset.h
index c9ff10bac..2cd28b507 100644
--- a/src/semiorderedset.h
+++ b/src/semiorderedset.h
@@ -27,6 +27,7 @@ namespace keydbutils
     template<>
     size_t hash(const sdsview &);
 }
+extern size_t g_semiOrderedSetTargetBucketSize;
 
 template<typename T, typename T_KEY = T, bool MEMMOVE_SAFE = false>
 class semiorderedset
@@ -41,11 +42,14 @@ class semiorderedset
     size_t idxRehash = (1ULL << bits_min); 
     int cfPauseRehash = 0;
 
-    constexpr size_t targetElementsPerBucket()
+    inline size_t targetElementsPerBucket()
     {
         // Aim for roughly 4 cache lines per bucket (determined by imperical testing)
         //  lower values are faster but use more memory
-        return std::max((64/sizeof(T))*8, (size_t)2);
+        if (g_semiOrderedSetTargetBucketSize == 0)
+            return std::max((64/sizeof(T))*8, (size_t)2);
+        else
+            return g_semiOrderedSetTargetBucketSize;
     }
 
 public: