如何确认RocksDB实际使用的内存分配器？

操作背景 #

按照官方指导，在Linux系统上为RocksDB配置更高效的非标准内存分配器（如jemalloc、tcmalloc），操作步骤如下：

# 示例：在Debian系统安装jemalloc
apt install -y libjemalloc-dev

# 启动Kafka Streams应用前设置LD_PRELOAD
export LD_PRELOAD="/usr/lib/x86_64-linux-gnu/libjemalloc.so"

但实际工作负载下，使用jemalloc后的内存消耗与未使用时完全一致（均为4.5GiB），换用tcmalloc后内存使用量也没有变化。于是通过分析动态链接库使用情况排查问题。

动态链接库分析结果 #

1. 查看RocksDB JNI库的依赖链接 #

执行命令：ldd /tmp/librocksdbjni16525886107314830425.so
输出：

linux-vdso.so.1 (0x00007fffc3ba6000)
    /usr/lib/x86_64-linux-gnu/libtcmalloc.so.4 (0x00007f5e50dff000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f5e51d94000)
    librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f5e51d8f000)
    libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f5e51d8a000)
    libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f5e50bd3000)
    libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f5e51ca1000)
    libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f5e51c81000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5e509aa000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f5e51d9f000)
    libunwind.so.8 => /lib/x86_64-linux-gnu/libunwind.so.8 (0x00007f5e51c66000)
    liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f5e51c3b000)

2. 检查RocksDB库中malloc相关符号 #

执行命令：objdump -T /tmp/librocksdbjni16525886107314830425.so | grep malloc
输出：

0000000000000000      DF *UND*  0000000000000000 (GLIBC_2.2.5) malloc_usable_size
0000000000000000      DF *UND*  0000000000000000 (GLIBC_2.2.5) malloc
0000000000000000  w   D  *UND*  0000000000000000              mallocx
0000000000000000  w   D  *UND*  0000000000000000              malloc_stats_print
0000000000558360  w   DF .text  00000000000000e2  Base        _ZN7rocksdb23JemallocNodumpAllocatorD1Ev
00000000002fedd0 g    DF .text  0000000000000093  Base        rocksdb_jemalloc_nodump_allocator_create
0000000000558360  w   DF .text  00000000000000e2  Base        _ZN7rocksdb23JemallocNodumpAllocatorD2Ev
0000000000bf85e0  w   DO .data.rel.ro   00000000000000c0  Base        _ZTVN7rocksdb23JemallocNodumpAllocatorE
0000000000557fa0 g    DF .text  00000000000002f7  Base        _ZN7rocksdb26NewJemallocNodumpAllocatorERNS_24JemallocAllocatorOptionsEPSt10shared_ptrINS_15MemoryAllocatorEE
0000000000557bd0 g    DF .text  000000000000015b  Base        _ZN7rocksdb23JemallocNodumpAllocatorC1ERNS_24JemallocAllocatorOptionsE
0000000000557d30 g    DF .text  0000000000000096  Base        _ZN7rocksdb23JemallocNodumpAllocator11IsSupportedEPSs
00000000005582d0  w   DF .text  0000000000000008  Base        _ZNK7rocksdb23JemallocNodumpAllocator4NameEv
0000000000557bd0 g    DF .text  000000000000015b  Base        _ZN7rocksdb23JemallocNodumpAllocatorC2ERNS_24JemallocAllocatorOptionsE
00000000007eb510 g    DF .text  0000000000000005  Base        _Z12toku_xmallocm
0000000000301fb0 g    DF .text  000000000000000b  Base        rocksdb_options_set_dump_malloc_stats
0000000000557dd0 g    DF .text  00000000000001c3  Base        _ZN7rocksdb23JemallocNodumpAllocator14PrepareOptionsERKNS_13ConfigOptionsE
00000000007ebe30 g    DF .text  00000000000000e5  Base        _ZN8memarena17malloc_from_arenaEm
0000000000558450  w   DF .text  00000000000000bb  Base        _ZN7rocksdb23JemallocNodumpAllocatorD0Ev

问题 #

尽管获取了以上分析结果，仍无法确定RocksDB是否实际使用了指定的内存分配器。

内容的提问来源于stack exchange，提问作者Andras Hatvani