Fix flaky SimCacheTest.SimCacheLogging (#9373)

Summary:
The random string may contain the string we're checking, e.g.:
```
ADD - 206FBC78E96BC4C6A2DDDDC0AD5D1ADD - 111
```
Only check the line starts-with "ADD -".

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9373

Test Plan: `gtest-parallel ./sim_cache_test --gtest_filter=SimCacheTest.SimCacheLogging -r 1000`

Reviewed By: riversand963

Differential Revision: D33519574

Pulled By: jay-zhuang

fbshipit-source-id: d0c1c9b0b489246d292e7da4133030edaa748099

utilities/simulator_cache/sim_cache.cc

@@ -6,6 +6,7 @@
 #include "rocksdb/utilities/sim_cache.h"
 
 #include <atomic>
+#include <iomanip>
 
 #include "file/writable_file_writer.h"
 #include "monitoring/statistics.h"
@@ -13,7 +14,6 @@
 #include "rocksdb/env.h"
 #include "rocksdb/file_system.h"
 #include "util/mutexlock.h"
-#include "util/string_util.h"
 
 namespace ROCKSDB_NAMESPACE {
 
@@ -68,11 +68,12 @@ class CacheActivityLogger {
       return;
     }
 
-    std::string log_line = "LOOKUP - " + key.ToString(true) + "\n";
-
+    std::ostringstream oss;
     // line format: "LOOKUP - <KEY>"
+    oss << "LOOKUP - " << key.ToString(true) << std::endl;
+
     MutexLock l(&mutex_);
-    Status s = file_writer_->Append(log_line);
+    Status s = file_writer_->Append(oss.str());
     if (!s.ok() && bg_status_.ok()) {
       bg_status_ = s;
     }
@@ -88,15 +89,11 @@ class CacheActivityLogger {
       return;
     }
 
-    std::string log_line = "ADD - ";
-    log_line += key.ToString(true);
-    log_line += " - ";
-    AppendNumberTo(&log_line, size);
-    log_line += "\n";
-
+    std::ostringstream oss;
     // line format: "ADD - <KEY> - <KEY-SIZE>"
+    oss << "ADD - " << key.ToString(true) << " - " << size << std::endl;
     MutexLock l(&mutex_);
-    Status s = file_writer_->Append(log_line);
+    Status s = file_writer_->Append(oss.str());
     if (!s.ok() && bg_status_.ok()) {
       bg_status_ = s;
     }
@@ -298,25 +295,23 @@ class SimCacheImpl : public SimCache {
   }
 
   std::string ToString() const override {
-    std::string res;
-    res.append("SimCache MISSes: " + std::to_string(get_miss_counter()) + "\n");
-    res.append("SimCache HITs:    " + std::to_string(get_hit_counter()) + "\n");
-    char buff[350];
+    std::ostringstream oss;
+    oss << "SimCache MISSes:  " << get_miss_counter() << std::endl;
+    oss << "SimCache HITs:    " << get_hit_counter() << std::endl;
     auto lookups = get_miss_counter() + get_hit_counter();
-    snprintf(buff, sizeof(buff), "SimCache HITRATE: %.2f%%\n",
-             (lookups == 0 ? 0 : get_hit_counter() * 100.0f / lookups));
-    res.append(buff);
-    return res;
+    oss << "SimCache HITRATE: " << std::fixed << std::setprecision(2)
+        << (lookups == 0 ? 0 : get_hit_counter() * 100.0f / lookups)
+        << std::endl;
+    return oss.str();
   }
 
   std::string GetPrintableOptions() const override {
-    std::string ret;
-    ret.reserve(20000);
-    ret.append("    cache_options:\n");
-    ret.append(cache_->GetPrintableOptions());
-    ret.append("    sim_cache_options:\n");
-    ret.append(key_only_cache_->GetPrintableOptions());
-    return ret;
+    std::ostringstream oss;
+    oss << "    cache_options:" << std::endl;
+    oss << cache_->GetPrintableOptions();
+    oss << "    sim_cache_options:" << std::endl;
+    oss << key_only_cache_->GetPrintableOptions();
+    return oss.str();
   }
 
   Status StartActivityLogging(const std::string& activity_log_file, Env* env,

utilities/simulator_cache/sim_cache_test.cc

@@ -177,23 +177,21 @@ TEST_F(SimCacheTest, SimCacheLogging) {
 
   std::string file_contents = "";
   ASSERT_OK(ReadFileToString(env_, log_file, &file_contents));
+  std::istringstream contents(file_contents);
 
   int lookup_num = 0;
   int add_num = 0;
-  std::string::size_type pos;
 
-  // count number of lookups
-  pos = 0;
-  while ((pos = file_contents.find("LOOKUP -", pos)) != std::string::npos) {
-    ++lookup_num;
-    pos += 1;
-  }
-
-  // count number of additions
-  pos = 0;
-  while ((pos = file_contents.find("ADD -", pos)) != std::string::npos) {
-    ++add_num;
-    pos += 1;
+  std::string line;
+  // count number of lookups and additions
+  while (std::getline(contents, line)) {
+    // check if the line starts with LOOKUP or ADD
+    if (line.rfind("LOOKUP -", 0) == 0) {
+      ++lookup_num;
+    }
+    if (line.rfind("ADD -", 0) == 0) {
+      ++add_num;
+    }
   }
 
   // We asked for every block twice