checkpoint and recovering process use too much memory

hi dears,

I had an asynchronous steaming replication HA cluster.Each node had 64G memory.pg is 9.6.2 and deployed on centos 6.

Last month the database was killed by OS kernel for OOM,the checkpoint process was killed.

I noticed checkpoint process occupied memory for more than 20GB，and it was growing everyday.In the hot-standby node,the recovering process occupied memory as big as checkpoint process.

I turned the checkpoint parameters,but it didn't worked.

Now In the standby node,checkpoint and recovering process used more then 50GB memory as below,and I worried someday the cluster would be killed by OS again.

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
167158 postgres 20 0 34.9g 25g 25g S 0.0 40.4 46:36.86 postgres: startup process recovering 00000004000008550000004B
167162 postgres 20 0 34.9g 25g 25g S 0.0 40.2 17:58.38 postgres: checkpointer process

shared_buffers = 32GB

and this is my checkpoint configuration:

checkpoint_timeout = 5min # range 30s-1d
max_wal_size = 3GB
min_wal_size = 1GB
checkpoint_completion_target = 0.6 # checkpoint target duration, 0.0 - 1.0
checkpoint_flush_after = 1MB # 0 disables,
# default is 256kB on linux, 0 otherwise
checkpoint_warning = 300s # 0 disables

in log file ,it started every 5 minites.

2017-11-02 16:55:14.063 CST,,,758087,,59e5b9c2.b9147,2498,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint complete: wrote 29416 buffers (0.7%); 0 transaction log file(s) added, 0 removed, 0 recycled; write=269.904 s, sync=0.017 s, total=269.930 s; sync files=86, longest=0.006 s, average=0.000 s; distance=235633 kB, estimate=816034 kB",,,,,,,,"LogCheckpointEnd, xlog.c:8121",""
2017-11-02 16:55:44.093 CST,,,758087,,59e5b9c2.b9147,2499,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint starting: time",,,,,,,,"LogCheckpointStart, xlog.c:8039",""
2017-11-02 16:59:13.824 CST,,,758087,,59e5b9c2.b9147,2500,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint complete: wrote 2091 buffers (0.0%); 0 transaction log file(s) added, 0 removed, 29 recycled; write=209.585 s, sync=0.072 s, total=209.731 s; sync files=46, longest=0.024 s, average=0.001 s; distance=11700 kB, estimate=735601 kB",,,,,,,,"LogCheckpointEnd, xlog.c:8121",""
2017-11-02 17:00:44.903 CST,,,758087,,59e5b9c2.b9147,2501,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint starting: time",,,,,,,,"LogCheckpointStart, xlog.c:8039",""
2017-11-02 17:05:14.249 CST,,,758087,,59e5b9c2.b9147,2502,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint complete: wrote 93078 buffers (2.2%); 0 transaction log file(s) added, 23 removed, 44 recycled; write=269.104 s, sync=0.023 s, total=269.346 s; sync files=109, longest=0.010 s, average=0.000 s; distance=480607 kB, estimate=710102 kB",,,,,,,,"LogCheckpointEnd, xlog.c:8121",""
2017-11-02 17:05:44.269 CST,,,758087,,59e5b9c2.b9147,2503,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint starting: time",,,,,,,,"LogCheckpointStart, xlog.c:8039",""
2017-11-02 17:10:14.215 CST,,,758087,,59e5b9c2.b9147,2504,,2017-10-17 16:05:22 CST,,0,LOG,00000,"checkpoint complete: wrote 177599 buffers (4.2%); 0 transaction log file(s) added, 0 removed, 53 recycled; write=269.728 s, sync=0.010 s, total=269.945 s; sync files=88, longest=0.004 s, average=0.000 s; distance=1140361 kB, estimate=1140361 kB",,,,,,,,"LogCheckpointEnd, xlog.c:8121",""

Pleas kindly let me know how could I reduce the 2 process memory usage.Many many thanks.