python - 流水线操作时 Redis 中的 MemoryError

Question

我正在使用此 Python 脚本将数据从一个 ElastiCache Redis 实例迁移到另一个实例。它使用 redis 流水线以 block 的形式迁移数据。

https://gist.github.com/thomasst/afeda8fe80534a832607

但是我得到了这个奇怪的错误:

Traceback (most recent call last):###########                                         | ETA:  0:00:12
  File "migrate-redis.py", line 95, in <module>
    migrate()
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 664, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 644, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 837, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 464, in invoke
    return callback(*args, **kwargs)
  File "migrate-redis.py", line 74, in migrate
    results = pipeline.execute(False)
  File "/usr/local/lib/python2.7/dist-packages/redis/client.py", line 2593, in execute
    return execute(conn, stack, raise_on_error)
  File "/usr/local/lib/python2.7/dist-packages/redis/client.py", line 2446, in _execute_transaction
    all_cmds = connection.pack_commands([args for args, _ in cmds])
  File "/usr/local/lib/python2.7/dist-packages/redis/connection.py", line 637, in pack_commands
    output.append(SYM_EMPTY.join(pieces))
MemoryError

RAM 没有问题，因为节点有 6 GB 的 RAM。

源码redis的Memory Profile如下:

used_memory:1483900120
used_memory_human:1.38G
used_memory_rss:1945829376
used_memory_peak:2431795528
used_memory_peak_human:2.26G
used_memory_lua:86016
mem_fragmentation_ratio:1.31
mem_allocator:jemalloc-3.6.0

这可能是什么原因造成的？

Answer 1

从你的错误日志来看，跟你的redis服务器没有关系。当您的 redis 客户端将所有命令打包到内存缓冲区时，会发生错误。

也许您可以尝试减少 migrate-redis.py 中的 SCAN 计数选项以测试它是否太大而无法打包。