官方说法提供的最后一招(last resort)就是WatchDog。它能够将慢操作的整个函数执行栈打印到Redis日志中。因为它与前面介绍过的将记录保存在内存中的延迟和满操作记录不同，所以记得使用前要在redis.conf中配置logfile日志路径：
- [root@vm redis-3.0.3]# src/redis-cli -h 127.0.0.1
- 127.0.0.1:6379> CONFIG SET watchdog-period 500
- OK
- 127.0.0.1:6379> debug sleep 1
- OK
- [root@vm redis-3.0.3]# tailf redis.log
- `-._ `-.__.-' _.-'
- `-._ _.-'
- `-.__.-'
- 51091:M 12 Aug 15:36:53.337 # Server started, Redis version 3.0.3
- 51091:M 12 Aug 15:36:53.338 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
- 51091:M 12 Aug 15:36:53.338 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
- 51091:M 12 Aug 15:36:53.343 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
- 51091:M 12 Aug 15:36:53.343 * DB loaded from disk: 0.000 seconds
- 51091:M 12 Aug 15:36:53.343 * The server is now ready to accept connections on port 6379
- 51091:signal-handler (1439365058)
- --- WATCHDOG TIMER EXPIRED ---
- src/redis-server 127.0.0.1:6379(logStackTrace+0x43)[0x450363]
- /lib64/libpthread.so.0(__nanosleep+0x2d)[0x3c0740ef3d]
- /lib64/libpthread.so.0[0x3c0740f710]
- /lib64/libpthread.so.0[0x3c0740f710]
- /lib64/libpthread.so.0(__nanosleep+0x2d)[0x3c0740ef3d]
- src/redis-server 127.0.0.1:6379(debugCommand+0x58d)[0x45180d]
- src/redis-server 127.0.0.1:6379(call+0x72)[0x4201b2]
- src/redis-server 127.0.0.1:6379(processCommand+0x3e5)[0x4207d5]
- src/redis-server 127.0.0.1:6379(processInputBuffer+0x4f)[0x42c66f]
- src/redis-server 127.0.0.1:6379(readQueryFromClient+0xc2)[0x42c7b2]
- src/redis-server 127.0.0.1:6379(aeProcessEvents+0x13c)[0x41a52c]
- src/redis-server 127.0.0.1:6379(aeMain+0x2b)[0x41a7eb]
- src/redis-server 127.0.0.1:6379(main+0x2cd)[0x423c8d]
- /lib64/libc.so.6(__libc_start_main+0xfd)[0x3c0701ed5d]
- src/redis-server 127.0.0.1:6379[0x419b49]
- 51091:signal-handler (51091:signal-handler (1439365058) ) --------
本文作者：geelou
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