add compaction log Summary:

Summary:
add compaction summary to log

log looks like:

2012/08/17-18:18:32.557334 7fdcaa2bb700 Compaction summary: Base level 0, input file:[11 9 7 ],[]

Test Plan: tested via db_test

Reviewers: dhruba

Differential Revision: https://reviews.facebook.net/D4749

db/db_impl.cc

@@ -890,6 +890,9 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
       compact->compaction->level(),
       compact->compaction->num_input_files(1),
       compact->compaction->level() + 1);
+  char scratch[200];
+  compact->compaction->Summary(scratch, 256);
+  Log(options_.info_log, "Compaction start summary: %s\n", scratch);
 
   assert(versions_->NumLevelFiles(compact->compaction->level()) > 0);
   assert(compact->builder == NULL);

db/version_set.cc

@@ -1443,4 +1443,37 @@ void Compaction::ReleaseInputs() {
   }
 }
 
+static void InputSummary(std::vector<FileMetaData*>& files,
+    char* output,
+    int len) {
+  int write = 0;
+  for (int i = 0; i < files.size(); i++) {
+    int sz = len - write;
+    int ret = snprintf(output + write, sz, "%llu(%llu) ",
+        files.at(i)->number,
+        files.at(i)->file_size);
+    if (ret < 0 || ret >= sz)
+      break;
+    write += ret;
+  }
+}
+
+void Compaction::Summary(char* output, int len) {
+  int write = snprintf(output, len, "Base level %d, inputs:", level_);
+  if(write < 0 || write > len)
+    return;
+
+  char level_low_summary[100];
+  InputSummary(inputs_[0], level_low_summary, 100);
+  char level_up_summary[100];
+  if (inputs_[1].size()) {
+    InputSummary(inputs_[1], level_up_summary, 100);
+  } else {
+    level_up_summary[0] = '\0';
+  }
+
+  snprintf(output + write, len - write, "[%s],[%s]",
+      level_low_summary, level_up_summary);
+}
+
 }  // namespace leveldb

db/version_set.h

@@ -344,6 +344,8 @@ class Compaction {
   // is successful.
   void ReleaseInputs();
 
+  void Summary(char* output, int len);
+
  private:
   friend class Version;
   friend class VersionSet;