tglogutil-compaction: add option --dry-run

docs/tglogutil-compaction-man.md

@@ -16,6 +16,8 @@ Specify the location set in the `log_location` parameter in the `[datastore]` se
 Options:
 * `--force=<bool>`
     * If `true`, do not prompt before processing (default `false`)
+* `--dry-run=<bool>`
+    * Dry run mode. If `true`, transaction log files are not modified (default `false`)
 * `--thread-num=<number>`
     * Number (default `1`) of concurrent processing thread of reading log files
 * `--working-dir=</path/to/working-dir>`

src/limestone/dblogutil/dblogutil.cpp

@@ -41,6 +41,7 @@ DEFINE_string(output_format, "human-readable", "format of output (human-readable
 
 // compaction
 DEFINE_bool(force, false, "(subcommand compaction) skip start prompt");
+DEFINE_bool(dry_run, false, "(subcommand compaction) dry run");
 DEFINE_string(working_dir, "", "(subcommand compaction) working directory");
 DEFINE_bool(make_backup, false, "(subcommand compaction) make backup of target dblogdir");
 
@@ -240,6 +241,13 @@ void compaction(dblog_scan &ds, std::optional<epoch_id_type> epoch) {
         throw std::runtime_error("I/O error");
     }
 
+    if (FLAGS_dry_run) {
+        std::cout << "compaction will be successfully completed (dry-run mode)" << std::endl;
+        VLOG_LP(log_info) << "deleting work directory " << tmp;
+        boost::filesystem::remove_all(tmp);
+        return;
+    }
+
     if (FLAGS_make_backup) {
         auto bkdir = make_backup_dir_next_to(from_dir);
         VLOG_LP(log_info) << "renaming " << from_dir << " to " << bkdir << " for backup";