With ldb --try_load_options and wal_dir doesn't exist, ignore it (#4875)

Summary:
LDB is frequently used to exam data copied. wal_dir in option file is not modified and it usually points to the path it copied from.
The user experience will be better if when ldb sees wal_dir pointed by the option file doesn't exist, rather than fail, just ignore it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4875

Differential Revision: D13643173

Pulled By: siying

fbshipit-source-id: 2e64d4ea2ec49a6794b9a706b7fc1ba901128bb8

HISTORY.md

@@ -9,6 +9,7 @@
 * Transaction::GetForUpdate is extended with a do_validate parameter with default value of true. If false it skips validating the snapshot before doing the read. Similarly ::Merge, ::Put, ::Delete, and ::SingleDelete are extended with assume_tracked with default value of false. If true it indicates that call is assumed to be after a ::GetForUpdate.
 * `TableProperties::num_entries` and `TableProperties::num_deletions` now also account for number of range tombstones.
 * Remove geodb, spatial_db, document_db, json_document, date_tiered_db, and redis_lists.
+* With "ldb ----try_load_options", when wal_dir specified by the option file doesn't exist, ignore it.
 
 ### Bug Fixes
 * Fix a deadlock caused by compaction and file ingestion waiting for each other in the event of write stalls.

tools/ldb_cmd.cc

@@ -332,6 +332,12 @@ void LDBCommand::OpenDB() {
       db_ = nullptr;
       return;
     }
+    if (options_.env->FileExists(options_.wal_dir).IsNotFound()) {
+      options_.wal_dir = db_path_;
+      fprintf(
+          stderr,
+          "wal_dir loaded from the option file doesn't exist. Ignore it.\n");
+    }
   }
   options_ = PrepareOptionsForOpenDB();
   if (!exec_state_.IsNotStarted()) {