Increase maximum read-only mmap()s used from 1000 to 4096 on 64-bit systems
Increase maximum read-only mmap()s used from 1000 to 4096 on 64-bit systems

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.

See https://github.com/bitcoin-core/leveldb/pull/19.

Original change by Clem Taylor. Ported to LevelDB 1.22 by Wladimir J.
van der Laan.

bitcoin-core/leveldb,bitcoin-core/leveldb,bitcoin-core/leveldb