Make db_stress Not purge redundant keys on some opens

Summary: In light of the new option introduced by commit 806e264350 where the database has an option to compact before flushing to disk, we want the stress test to test both sides of the option. Have made it to 'deterministically' and configurably change that option for reopens.

Test Plan: make db_stress; ./db_stress with some differnet options

Reviewers: dhruba, vamsi

Reviewed By: dhruba

CC: leveldb, sheki

Differential Revision: https://reviews.facebook.net/D9165

tools/db_stress.cc

@@ -158,6 +158,9 @@ static uint32_t FLAGS_ops_per_thread = 600000;
 // Log2 of number of keys per lock
 static uint32_t FLAGS_log2_keys_per_lock = 2; // implies 2^2 keys per lock
 
+// Percentage of times we want to purge redundant keys in memory before flushing
+static uint32_t FLAGS_purge_redundant_percent = 50;
+
 extern bool useOsBuffer;
 extern bool useFsReadAhead;
 extern bool useMmapRead;
@@ -843,6 +846,8 @@ class StressTest {
     fprintf(stdout, "Num times DB reopens: %d\n", FLAGS_reopen);
     fprintf(stdout, "Batches/snapshots   : %d\n",
             FLAGS_test_batches_snapshots);
+    fprintf(stdout, "Purge redundant %%   : %d\n",
+            FLAGS_purge_redundant_percent);
     fprintf(stdout, "Num keys per lock   : %d\n",
             1 << FLAGS_log2_keys_per_lock);
 
@@ -894,6 +899,10 @@ class StressTest {
     options.delete_obsolete_files_period_micros =
       FLAGS_delete_obsolete_files_period_micros;
     options.max_manifest_file_size = 1024;
+    static Random purge_percent(1000); // no benefit from non-determinism here
+    if (purge_percent.Uniform(100) < FLAGS_purge_redundant_percent - 1) {
+      options.purge_redundant_kvs_while_flush = false;
+    }
     Status s = DB::Open(options, FLAGS_db, &db_);
     if (!s.ok()) {
       fprintf(stderr, "open error: %s\n", s.ToString().c_str());
@@ -1066,6 +1075,9 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--delete_obsolete_files_period_micros=%ld%c",
                       &l, &junk) == 1) {
       FLAGS_delete_obsolete_files_period_micros = n;
+    } else if (sscanf(argv[i], "--purge_redundant_percent=%d%c", &n, &junk) == 1
+        && (n >= 0 && n <= 100)) {
+      FLAGS_purge_redundant_percent = n;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);