crash_test to trigger fail points other than file appending more frequently

Summary:
For half of the crash_test run, disable fail point for file appending, in order to trigger other fail point more frequently.
Also, tune crash test parameter a little bit for it to initialize faster.

Test Plan: Run crash_test and make sure it issues db_stress commands as expected.

Reviewers: yhchiang, igor, rven, anthony, IslamAbdelRahman, kradhakrishnan

Reviewed By: kradhakrishnan

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D48843

tools/db_crashtest2.py

@@ -71,6 +71,7 @@ def main(argv):
 
     total_check_mode = 4
     check_mode = 0
+    kill_mode = 0
 
     test_tmpdir = os.environ.get("TEST_TMPDIR")
     if test_tmpdir is None or test_tmpdir == "":
@@ -83,7 +84,19 @@ def main(argv):
         killoption = ""
         if check_mode == 0:
             # run with kill_random_test
+            if kill_mode == 0:
                 killoption = " --kill_random_test=" + str(kill_random_test)
+            elif kill_mode == 1:
+                # Remove kill point for normal reads and reduce kill odds
+                # by 3, so that it still runs about one minutes in average
+                # before hitting a crash point.
+                killoption = " --kill_random_test=" + \
+                             str(kill_random_test / 3 + 1)
+                killoption += \
+                    " --kill_prefix_blacklist=WritableFileWriter::Append," \
+                    "WritableFileWriter::WriteBuffered"
+            # Run kill mode 0 and 1 by turn.
+            kill_mode = (kill_mode + 1) % 2
             # use large ops per thread since we will kill it anyway
             additional_opts = "--ops_per_thread=" + \
                               str(100 * ops_per_thread) + killoption
@@ -133,6 +146,8 @@ def main(argv):
                 --filter_deletes=%s
                 --memtablerep=skip_list
                 --prefix_size=0
+                --nooverwritepercent=1
+                --log2_keys_per_lock=10
                  %s
                 """ % (threads,
                        write_buf_size,
@@ -172,6 +187,8 @@ def main(argv):
                 --filter_deletes=%s
                 --memtablerep=prefix_hash
                 --prefix_size=7
+                --nooverwritepercent=1
+                --log2_keys_per_lock=10
                 %s
                 """ % (random.randint(0, 1),
                        threads,