wl2077 - scan optimizations

(recommit in clean clone)


ndb/src/kernel/blocks/dbdih/Dbdih.hpp:
  removed unused variable
ndb/src/kernel/blocks/dbdih/DbdihMain.cpp:
  Always give all nodes in DIGETPRIMREQ
ndb/src/kernel/blocks/dbtc/DbtcMain.cpp:
  Allow readcommited-scans to scan backup fragments
ndb/test/ndbapi/testReadPerf.cpp:
  better printous

ndb/docs/wl2077.txt

@@ -0,0 +1,35 @@
+
+100' * (select 1 from T1 (1M rows) where key = rand());
+1 host, 1 ndbd, api co-hosted
+results in 1000 rows / sec
+
+		       wo/reset bounds  w/ rb
+4.1-read committed     a) 4.9		b) 7.4
+4.1-read hold lock     c) 4.7		d) 6.7
+
+wl2077-read committed  6.4 (+30%)	10.8 (+45%)
+wl2077-read hold lock  4.6 (-1%)	6.7 (+ 0%)
+
+-- Comparision e)
+serial pk:	       10.9'
+batched (1000):	       59'
+serial uniq index:     8.4'
+batched (1000):	       33'
+index range (1000):    186'
+
+----
+
+load) testScanPerf -c 1 -d 1 T1
+a) testScanPerf -s 100000 -c 0 -d 0 -a 1 -l 0 -r 2 -q 0 T1
+b) testScanPerf -s 100000 -c 0 -d 0 -a 1 -l 0 -r 2 -q 1 T1
+c) testScanPerf -s 100000 -c 0 -d 0 -a 1 -l 1 -r 2 -q 0 T1
+d) testScanPerf -s 100000 -c 0 -d 0 -a 1 -l 1 -r 2 -q 1 T1
+e) testReadPerf -i 25 -c 0 -d 0 T1
+
+--- music join		1db-co		2db-co
+			
+4.1			13s		14s
+4.1 wo/ blobs		1.7s		3.2s
+
+wl2077			12s		14s
+wl2077 wo/ blobs	1.2s (-30%)	2.5s (-22%)