Merge bitcoin#30039: dbwrapper: Bump LevelDB max file size to 32 MiB to avoid system slowdown from high disk cache flush rate

b73d331 dbwrapper: Bump max file size to 32 MiB (Maciej S. Szmigiero)

Pull request description:

  The default max file size for LevelDB is 2 MiB, which results in the LevelDB compaction code generating ~4 disk cache flushes per second when syncing with the Bitcoin network.
  These disk cache flushes are triggered by `fdatasync()` syscall issued by the LevelDB compaction code when reaching the max file size.

  If the database is on a HDD this flush rate brings the whole system to a crawl.
  It also results in very slow throughput since 2 MiB * 4 flushes per second is about 8 MiB / second max throughput, while even an old HDD can pull 100 - 200 MiB / second streaming throughput.

  Increase the max file size for LevelDB to 128 MiB instead so the flush rate drops to about 1 flush / 2 seconds and the system no longer gets so sluggish.

  The max file size value chosen also matches the `MAX_BLOCKFILE_SIZE` file size setting already used by the block storage.

ACKs for top commit:
  l0rinc:
    ACK b73d331
  davidgumberg:
    ACK bitcoin@b73d331
  andrewtoth:
    ACK b73d331
  TheCharlatan:
    ACK b73d331
  willcl-ark:
    ACK b73d331
  tdb3:
    ACK b73d331
  laanwj:
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Tree-SHA512: 5d8fb9ad1ea643fb3e42a9c59f6fc90cc5cc3b82c06d9b8d59de3a5a926fabaeb78efb51b608b1e7925f49d82dfcbd5b72c552993879789f33201efe57c278f3

Author: fanquake

src/dbwrapper.cpp

@@ -147,6 +147,7 @@ static leveldb::Options GetOptions(size_t nCacheSize)
         // on corruption in later versions.
         options.paranoid_checks = true;
     }
+    options.max_file_size = std::max(options.max_file_size, DBWRAPPER_MAX_FILE_SIZE);
     SetMaxOpenFiles(&options);
     return options;
 }

src/dbwrapper.h

@@ -22,6 +22,7 @@
 
 static const size_t DBWRAPPER_PREALLOC_KEY_SIZE = 64;
 static const size_t DBWRAPPER_PREALLOC_VALUE_SIZE = 1024;
+static const size_t DBWRAPPER_MAX_FILE_SIZE = 32 << 20; // 32 MiB
 
 //! User-controlled performance and debug options.
 struct DBOptions {