rocksdb: use max_manifest_file_size option

Cockroach uses a single long running rocksdb instance for the entire
process lifetime, which could be many months. By default, rocksdb tracks
filesystem state changes in a log file called the MANIFEST, which grows
without bound until the instance is re-opened. We should bound the
maximum file size of rocksdb MANIFEST using the corresponding rocksdb
option to prevent unbounded growth.

The MANIFEST file grew to several GBs in size in a customer bug report
but that was probably because of some other bad behavior in rocksdb
state management. We do want to bound the MANIFEST size in such cases as
well.

Release note: None

c-deps/libroach/options.cc

@@ -262,6 +262,12 @@ rocksdb::Options DBMakeOptions(DBOptions db_opts) {
   options.target_file_size_base = 4 << 20;  // 4 MB
   options.target_file_size_multiplier = 2;
 
+  // Because we open a long running rocksdb instance, we do not want the
+  // manifest file to grow unbounded. Assuming each manifest entry is about 1
+  // KB, this allows for 128 K entries. This could account for several hours to
+  // few months of runtime without rolling based on the workload.
+  options.max_manifest_file_size = 128 << 20;  // 128 MB
+
   rocksdb::BlockBasedTableOptions table_options;
   if (db_opts.cache != nullptr) {
     table_options.block_cache = db_opts.cache->rep;