perf(alloc): use jemalloc to reduce memory fragmentation

  Replace the system allocator (glibc malloc) with jemalloc via
  tikv-jemallocator. Reduces RSS by ~18% by eliminating malloc
  fragmentation that accumulates over time with RocksDB's allocation
  patterns.

Author: EddieHouston

Cargo.lock

@@ -49,6 +49,7 @@ page_size = "0.6.0"
 prometheus = "0.14"
 rayon = "1.5.0"
 rocksdb = "0.24"
+tikv-jemallocator = "0.6"
 rust-crypto = "0.2"
 serde = "1.0.118"
 serde_derive = "1.0.118"

Cargo.toml

@@ -1,3 +1,6 @@
+#[global_allocator]
+static GLOBAL: tikv_jemallocator::Jemalloc = tikv_jemallocator::Jemalloc;
+
 extern crate error_chain;
 #[macro_use]
 extern crate log;