Merge bitpay#19: Increase maximum read-only mmap()s used from 1000 to…

… 4096 on 64-bit systems

4874cb8 Increase maximum number of read-only mmap()s used from 1000 to 4096 on 64 bit systems. (Clem Taylor)

Pull request description:

  By default LevelDB will only mmap() up to 1000 ldb files for reading and then fall back
  to using file desciptors.

  The typical linux system has a 'vm.max_map_count = 65530', so mapping only 1000 files
  seems arbitarily small. Increase this value to another arbitrarily small value, 4096.

Tree-SHA512: 42d0978f229603aa882ac47a43ec455be0e27c9c3e4d7e36f7e6b49bab6da7c1bd0d3ffbaca22dfda2a5722fa533d1ce7439e9f99fdedb64df0c4442bbb6a93c

util/env_posix.cc

@@ -585,8 +585,8 @@ static int MaxMmaps() {
   if (mmap_limit >= 0) {
     return mmap_limit;
   }
-  // Up to 1000 mmaps for 64-bit binaries; none for smaller pointer sizes.
-  mmap_limit = sizeof(void*) >= 8 ? 1000 : 0;
+  // Up to 4096 mmaps for 64-bit binaries; none for smaller pointer sizes.
+  mmap_limit = sizeof(void*) >= 8 ? 4096 : 0;
   return mmap_limit;
 }