Minor compaction logging improvements

1) make summary less likely to be truncated
2) format human-readable file sizes in summary
3) log the motivation for each universal compaction

db/compaction.cc

@@ -174,14 +174,37 @@ void Compaction::ResetNextCompactionIndex() {
   input_version_->ResetNextCompactionIndex(level_);
 }
 
+/*
+for sizes >=10TB, print "XXTB"
+for sizes >=10GB, print "XXGB"
+etc.
+*/
+static void FileSizeSummary(unsigned long long sz, char* output, int len) {
+  const unsigned long long ull10 = 10;
+  if (sz >= ull10<<40) {
+    snprintf(output, len, "%lluTB", sz>>40);
+  } else if (sz >= ull10<<30) {
+    snprintf(output, len, "%lluGB", sz>>30);
+  } else if (sz >= ull10<<20) {
+    snprintf(output, len, "%lluMB", sz>>20);
+  } else if (sz >= ull10<<10) {
+    snprintf(output, len, "%lluKB", sz>>10);
+  } else {
+    snprintf(output, len, "%lluB", sz);
+  }
+}
+
 static void InputSummary(std::vector<FileMetaData*>& files, char* output,
                          int len) {
   int write = 0;
   for (unsigned int i = 0; i < files.size(); i++) {
     int sz = len - write;
-    int ret = snprintf(output + write, sz, "%lu(%lu) ",
-        (unsigned long)files.at(i)->number,
-        (unsigned long)files.at(i)->file_size);
+    int ret;
+    char sztxt[16];
+    FileSizeSummary((unsigned long long)files.at(i)->file_size, sztxt, 16);
+    ret = snprintf(output + write, sz, "%lu(%s) ",
+                   (unsigned long)files.at(i)->number,
+                   sztxt);
     if (ret < 0 || ret >= sz)
       break;
     write += ret;
@@ -198,9 +221,9 @@ void Compaction::Summary(char* output, int len) {
     return;
   }
 
-  char level_low_summary[100];
+  char level_low_summary[1024];
   InputSummary(inputs_[0], level_low_summary, sizeof(level_low_summary));
-  char level_up_summary[100];
+  char level_up_summary[1024];
   if (inputs_[1].size()) {
     InputSummary(inputs_[1], level_up_summary, sizeof(level_up_summary));
   } else {

db/compaction_picker.cc

@@ -551,22 +551,27 @@ Compaction* UniversalCompactionPicker::PickCompaction(Version* version) {
       version->LevelFileSummary(&tmp, 0));
 
   // Check for size amplification first.
-  Compaction* c = PickCompactionUniversalSizeAmp(version, score);
-  if (c == nullptr) {
+  Compaction* c;
+  if ((c = PickCompactionUniversalSizeAmp(version, score)) != nullptr) {
+    Log(options_->info_log, "Universal: compacting for size amp\n");
+  } else {
 
     // Size amplification is within limits. Try reducing read
     // amplification while maintaining file size ratios.
     unsigned int ratio = options_->compaction_options_universal.size_ratio;
-    c = PickCompactionUniversalReadAmp(version, score, ratio, UINT_MAX);
 
-    // Size amplification and file size ratios are within configured limits.
-    // If max read amplification is exceeding configured limits, then force
-    // compaction without looking at filesize ratios and try to reduce
-    // the number of files to fewer than level0_file_num_compaction_trigger.
-    if (c == nullptr) {
+    if ((c = PickCompactionUniversalReadAmp(version, score, ratio, UINT_MAX)) != nullptr) {
+      Log(options_->info_log, "Universal: compacting for size ratio\n");
+    } else {
+      // Size amplification and file size ratios are within configured limits.
+      // If max read amplification is exceeding configured limits, then force
+      // compaction without looking at filesize ratios and try to reduce
+      // the number of files to fewer than level0_file_num_compaction_trigger.
       unsigned int num_files = version->files_[level].size() -
                                options_->level0_file_num_compaction_trigger;
-      c = PickCompactionUniversalReadAmp(version, score, UINT_MAX, num_files);
+      if ((c = PickCompactionUniversalReadAmp(version, score, UINT_MAX, num_files)) != nullptr) {
+        Log(options_->info_log, "Universal: compacting for file num\n");
+      }
     }
   }
   if (c == nullptr) {

db/db_impl.cc

@@ -2232,7 +2232,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact,
       compact->compaction->output_level(),
       compact->compaction->score(),
       options_.max_background_compactions - bg_compaction_scheduled_);
-  char scratch[256];
+  char scratch[2345];
   compact->compaction->Summary(scratch, sizeof(scratch));
   Log(options_.info_log, "Compaction start summary: %s\n", scratch);