erts: Reduce ets hash load factor

for faster lookup/insert/delete
at the expense of about one word per object.

2 files changed, 33 insertions, 22 deletions

diff --git a/erts/emulator/beam/erl_db_hash.c b/erts/emulator/beam/erl_db_hash.c
index 2d24f438ca..1752ec5191 100644
--- a/erts/emulator/beam/erl_db_hash.c
+++ b/erts/emulator/beam/erl_db_hash.c
@@ -87,7 +87,8 @@
 /* 
  * The following symbols can be manipulated to "tune" the linear hash array 
  */
-#define CHAIN_LEN 6                 /* Medium bucket chain len      */
+#define GROW_LIMIT(NACTIVE) ((NACTIVE)*1)
+#define SHRINK_LIMIT(NACTIVE) ((NACTIVE) / 2)
 
 /*
 ** We want the first mandatory segment to be small (to reduce minimal footprint)
@@ -434,7 +435,7 @@ db_finalize_dbterm_hash(int cret, DbUpdateHandle* handle);
 static ERTS_INLINE void try_shrink(DbTableHash* tb)
 {
     int nactive = NACTIVE(tb);
-    if (nactive > FIRST_SEGSZ && NITEMS(tb) < (nactive * CHAIN_LEN)
+    if (nactive > FIRST_SEGSZ && NITEMS(tb) < SHRINK_LIMIT(nactive)
 	&& !IS_FIXED(tb)) {
 	shrink(tb, nactive);
     }
@@ -837,7 +838,7 @@ Lnew:
     WUNLOCK_HASH(lck);
     {
 	int nactive = NACTIVE(tb);       
-	if (nitems > nactive * (CHAIN_LEN+1) && !IS_FIXED(tb)) {
+	if (nitems > GROW_LIMIT(nactive) && !IS_FIXED(tb)) {
 	    grow(tb, nactive);
 	}
     }
@@ -2891,7 +2892,7 @@ db_finalize_dbterm_hash(int cret, DbUpdateHandle* handle)
             WUNLOCK_HASH(lck);
             nactive = NACTIVE(tb);
 
-            if (nitems > nactive * (CHAIN_LEN + 1) && !IS_FIXED(tb)) {
+            if (nitems > GROW_LIMIT(nactive) && !IS_FIXED(tb)) {
                 grow(tb, nactive);
             }
         } else {
diff --git a/lib/stdlib/test/ets_SUITE.erl b/lib/stdlib/test/ets_SUITE.erl
index b02d17bdb6..6835e745bc 100644
--- a/lib/stdlib/test/ets_SUITE.erl
+++ b/lib/stdlib/test/ets_SUITE.erl
@@ -607,11 +607,11 @@ memory(Config) when is_list(Config) ->
 memory_do(Opts) ->
     L = [T1,T2,T3,T4] = fill_sets_int(1000,Opts),
     XR1 = case mem_mode(T1) of
-	      {normal,_} ->     {13836,13046,13046,13052}; %{13862,13072,13072,13078};
-	      {compressed,4} -> {11041,10251,10251,10252}; %{11067,10277,10277,10278};
-	      {compressed,8} -> {10050,9260,9260,9260} %{10076,9286,9286,9286}
+	      {normal,_} ->     {13836, 15346, 15346, 15346+6};
+	      {compressed,4} -> {11041, 12551, 12551, 12551+1};
+	      {compressed,8} -> {10050, 11560, 11560, 11560}
 	  end,
-    XRes1 = adjust_xmem(L, XR1),
+    XRes1 = adjust_xmem(L, XR1, 1),
     Res1 = {?S(T1),?S(T2),?S(T3),?S(T4)},
     lists:foreach(fun(T) ->
 			  Before = ets:info(T,size),
@@ -623,11 +623,11 @@ memory_do(Opts) ->
 		  end,
 		  L),
     XR2 = case mem_mode(T1) of
-	      {normal,_} ->     {13826,13037,13028,13034}; %{13852,13063,13054,13060};
-	      {compressed,4} -> {11031,10242,10233,10234}; %{11057,10268,10259,10260};
-	      {compressed,8} -> {10040,9251,9242,9242}     %10066,9277,9268,9268}
+	      {normal,_} ->     {13826, 15337, 15337-9, 15337-3};
+	      {compressed,4} -> {11031, 12542, 12542-9, 12542-8};
+	      {compressed,8} -> {10040, 11551, 11551-9, 11551-9}
 	  end,
-    XRes2 = adjust_xmem(L, XR2),
+    XRes2 = adjust_xmem(L, XR2, 1),
     Res2 = {?S(T1),?S(T2),?S(T3),?S(T4)},
     lists:foreach(fun(T) ->
 			  Before = ets:info(T,size),
@@ -639,17 +639,17 @@ memory_do(Opts) ->
 		  end,
 		  L),
     XR3 = case mem_mode(T1) of
-	      {normal,_} ->     {13816,13028,13010,13016}; %{13842,13054,13036,13042};
-	      {compressed,4} -> {11021,10233,10215,10216}; %{11047,10259,10241,10242};
-	      {compressed,8} -> {10030,9242,9224,9224} %{10056,9268,9250,9250}
+	      {normal,_} ->     {13816, 15328, 15328-18, 15328-12};
+	      {compressed,4} -> {11021, 12533, 12533-18, 12533-17};
+	      {compressed,8} -> {10030, 11542, 11542-18, 11542-18}
 	  end,
-    XRes3 = adjust_xmem(L, XR3),
+    XRes3 = adjust_xmem(L, XR3, 1),
     Res3 = {?S(T1),?S(T2),?S(T3),?S(T4)},
     lists:foreach(fun(T) ->
 			  ets:delete_all_objects(T)
 		  end,
 		  L),
-    XRes4 = adjust_xmem(L, {50,260,260,260}), %{76,286,286,286}),
+    XRes4 = adjust_xmem(L, {50, 256, 256, 256}, 0),
     Res4 = {?S(T1),?S(T2),?S(T3),?S(T4)},
     lists:foreach(fun(T) ->
 			  ets:delete(T)
@@ -660,7 +660,7 @@ memory_do(Opts) ->
 			  ets:select_delete(T,[{'_',[],[true]}])
 		  end,
 		  L2),
-    XRes5 = adjust_xmem(L2, {50,260,260,260}), %{76,286,286,286}),
+    XRes5 = adjust_xmem(L2, {50, 256, 256, 256}, 0),
     Res5 = {?S(T11),?S(T12),?S(T13),?S(T14)},
     io:format("XRes1 = ~p~n"
 	      " Res1 = ~p~n~n"
@@ -701,12 +701,22 @@ chk_normal_tab_struct_size() ->
     io:format("?TAB_STRUCT_SZ=~p~n", [?TAB_STRUCT_SZ]),
     ok.
 
-adjust_xmem([_T1,_T2,_T3,_T4], {A0,B0,C0,D0} = _Mem0) ->
+sizeof_ext_segtab() ->
+    case {erlang:system_info(wordsize),
+	  erlang:system_info(smp_support)} of
+	{4,true} -> 5 + 3;
+	{4,false} -> 3 + 3;
+	{8,true} -> 4 + 2;
+	{8,false} -> 3 + 2
+    end.
+
+adjust_xmem([_T1,_T2,_T3,_T4], {A0,B0,C0,D0} = _Mem0, EstCnt) ->
     %% Adjust for 64-bit, smp, and os:
     %%   Table struct size may differ.
 
     TabDiff = ?TAB_STRUCT_SZ,
-    {A0+TabDiff, B0+TabDiff, C0+TabDiff, D0+TabDiff}.
+    HTabDiff = TabDiff + EstCnt*sizeof_ext_segtab(),
+    {A0+TabDiff, B0+HTabDiff, C0+HTabDiff, D0+HTabDiff}.
 
 %% Misc. whitebox tests
 t_whitebox(Config) when is_list(Config) ->    
@@ -5363,12 +5373,12 @@ verify_table_load(T) ->
     Stats = ets:info(T,stats),
     {Buckets,AvgLen,StdDev,ExpSD,_MinLen,_MaxLen,_} = Stats,
     ok = if
-	     AvgLen > 7 ->
+	     AvgLen > 1.2 ->
 		 io:format("Table overloaded: Stats=~p\n~p\n",
 			   [Stats, ets:info(T)]),
 		 false;
 
-	     Buckets>256, AvgLen < 6 ->
+	     Buckets>256, AvgLen < 0.47 ->
 		 io:format("Table underloaded: Stats=~p\n~p\n",
 			   [Stats, ets:info(T)]),
 		 false;