Fix table-cache size bug, gather table-cache statistics and prevent readahead done by fs. Summary:

Summary:
The db_bench test was not using the specified value for the max-file-open. Fixed.

The fs readhead is switched off.

Gather statistics about the table cache and print it out at the end of the tets run.

Test Plan: Revert Plan:

Reviewers: adsharma, sc

Reviewed By: adsharma

Differential Revision: https://reviews.facebook.net/D3441

db/db_bench.cc

@@ -7,10 +7,12 @@
 #include <stdlib.h>
 #include "db/db_impl.h"
 #include "db/version_set.h"
+#include "db/db_statistics.h"
 #include "leveldb/cache.h"
 #include "leveldb/db.h"
 #include "leveldb/env.h"
 #include "leveldb/write_batch.h"
+#include "leveldb/statistics.h"
 #include "port/port.h"
 #include "util/crc32c.h"
 #include "util/histogram.h"
@@ -110,6 +112,10 @@ static int FLAGS_cache_numshardbits = -1;
 // Verify checksum for every block read from storage
 static bool FLAGS_verify_checksum = false;
 
+// Database statistics
+static bool FLAGS_statistics = false;
+static class leveldb::DBStatistics* dbstats = NULL;
+
 extern bool useOsBuffer;
 
 namespace leveldb {
@@ -398,6 +404,15 @@ class Benchmark {
 #endif
   }
 
+  void PrintStatistics() {
+    if (FLAGS_statistics) {
+      fprintf(stdout, "File opened:%ld closed:%ld errors:%ld\n",
+              dbstats->getNumFileOpens(),
+              dbstats->getNumFileCloses(),
+              dbstats->getNumFileErrors());
+    }
+  }
+
  public:
   Benchmark()
   : cache_(FLAGS_cache_size >= 0 ? 
@@ -542,6 +557,7 @@ class Benchmark {
         RunBenchmark(num_threads, name, method);
       }
     }
+    PrintStatistics();
   }
 
  private:
@@ -710,6 +726,8 @@ class Benchmark {
     options.block_cache = cache_;
     options.write_buffer_size = FLAGS_write_buffer_size;
     options.filter_policy = filter_policy_;
+    options.max_open_files = FLAGS_open_files;
+    options.statistics = dbstats;
     Status s = DB::Open(options, FLAGS_db, &db_);
     if (!s.ok()) {
       fprintf(stderr, "open error: %s\n", s.ToString().c_str());
@@ -983,6 +1001,12 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--bufferedio=%d%c", &n, &junk) == 1 &&
                (n == 0 || n == 1)) {
       useOsBuffer = n;
+    } else if (sscanf(argv[i], "--statistics=%d%c", &n, &junk) == 1 &&
+               (n == 0 || n == 1)) {
+      if (n == 1) {
+        dbstats = new leveldb::DBStatistics();
+        FLAGS_statistics = true;
+      }
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);

db/db_statistics.h

@@ -0,0 +1,36 @@
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#include <stdlib.h>
+#include "leveldb/statistics.h"
+#include "port/port.h"
+#include "util/mutexlock.h"
+
+namespace leveldb {
+
+class DBStatistics: public Statistics {
+ public:
+  DBStatistics() { }
+
+  void incNumFileOpens() {
+    MutexLock l(&mu_);
+    numFileOpens_++;
+  }
+
+  void incNumFileCloses() {
+    MutexLock l(&mu_);
+    numFileCloses_++;
+  }
+
+  void incNumFileErrors() {
+    MutexLock l(&mu_);
+    numFileErrors_++;
+  }
+
+ private:
+    port::Mutex mu_;
+};
+}
+
+

db/table_cache.cc

@@ -5,6 +5,7 @@
 #include "db/table_cache.h"
 
 #include "db/filename.h"
+#include "db/db_statistics.h"
 #include "leveldb/env.h"
 #include "leveldb/table.h"
 #include "util/coding.h"
@@ -16,10 +17,13 @@ struct TableAndFile {
   Table* table;
 };
 
+static class DBStatistics* dbstatistics;
+
 static void DeleteEntry(const Slice& key, void* value) {
   TableAndFile* tf = reinterpret_cast<TableAndFile*>(value);
   delete tf->table;
   delete tf->file;
+  dbstatistics ? dbstatistics->incNumFileCloses() : (void)0;
   delete tf;
 }
 
@@ -36,6 +40,7 @@ TableCache::TableCache(const std::string& dbname,
       dbname_(dbname),
       options_(options),
       cache_(NewLRUCache(entries)) {
+  dbstatistics = (DBStatistics*)options->statistics;
 }
 
 TableCache::~TableCache() {
@@ -48,12 +53,14 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
   char buf[sizeof(file_number)];
   EncodeFixed64(buf, file_number);
   Slice key(buf, sizeof(buf));
+  DBStatistics* stats = (DBStatistics*) options_->statistics;
   *handle = cache_->Lookup(key);
   if (*handle == NULL) {
     std::string fname = TableFileName(dbname_, file_number);
     RandomAccessFile* file = NULL;
     Table* table = NULL;
     s = env_->NewRandomAccessFile(fname, &file);
+    stats ? stats->incNumFileOpens() : (void)0;
     if (s.ok()) {
       s = Table::Open(*options_, file, file_size, &table);
     }
@@ -61,6 +68,7 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
     if (!s.ok()) {
       assert(table == NULL);
       delete file;
+      stats ? stats->incNumFileErrors() : (void)0;
       // We do not cache error results so that if the error is transient,
       // or somebody repairs the file, we recover automatically.
     } else {

include/leveldb/options.h

@@ -15,6 +15,7 @@ class Env;
 class FilterPolicy;
 class Logger;
 class Snapshot;
+class Statistics;
 
 // DB contents are stored in a set of blocks, each of which holds a
 // sequence of key,value pairs.  Each block may be compressed before
@@ -135,6 +136,9 @@ struct Options {
   // Default: NULL
   const FilterPolicy* filter_policy;
 
+  // If non-null, then we should collect metrics about database operations
+  Statistics* statistics;
+
   // Create an Options object with default values for all fields.
   Options();
 };

include/leveldb/statistics.h

@@ -0,0 +1,33 @@
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#ifndef STORAGE_LEVELDB_INCLUDE_STATISTICS_H_
+#define STORAGE_LEVELDB_INCLUDE_STATISTICS_H_
+
+namespace leveldb {
+
+// Analyze the performance of a db
+class Statistics {
+ public: 
+  // Create an Statistics object with default values for all fields.
+  Statistics() : numFileOpens_(0), numFileCloses_(0),
+                 numFileErrors_(0) {}
+
+  virtual void incNumFileOpens() = 0;
+  virtual void incNumFileCloses() = 0;
+  virtual void incNumFileErrors() = 0;
+
+  virtual long getNumFileOpens() { return numFileOpens_;}
+  virtual long getNumFileCloses() { return numFileCloses_;}
+  virtual long getNumFileErrors() { return numFileErrors_;}
+
+ protected:
+  long numFileOpens_;
+  long numFileCloses_;
+  long numFileErrors_;
+};
+
+}  // namespace leveldb
+
+#endif  // STORAGE_LEVELDB_INCLUDE_STATISTICS_H_