Streaming replication stacked.

Hi All,

I use streaming replication on systems.
But I have an problem.
I need your support.

The system sometimes stacks Postgres process.
So, postgresql data isn't syncing.

I checkd process that it was stacked "waiting" status on slave server.

e.g.) postgres: startup process recovering 0000000100000xxxxxxxxxx
waiting

And I think Master Server completed to transfer wal files but Slave
server couldn't read wal files.
In addition once about 10 hours later , suddenly waiting process
started .

Below is the replication status.

-----------------------------------------
state | streaming
sent_location | A3C/10D51570
write_location | A3C/10D51570
flush_location | A3C/10D51570
replay_location | A3C/10D4A4B8
sync_priority | 0
sync_state | async
-----------------------------------------

Replay_location was stopping and Other location was active.

And There is System Version.
-----------------------------------------
- PostgreSQL Version : 9.4
- OS : CentOS6.4
- Replicaion Type : async
-----------------------------------------

And Below is the Postgres configration.
-----------------------------------------
++ Master :
wal_level = hot_standby
wal_buffers = 16MB
checkpoint_segments = 32
checkpoint_completion_target = 0.7
archive_mode = on
archive_command = 'cp %p /var/lib/pgsql/9.4/data/archive_log/%f'
max_wal_senders = 3
wal_keep_segments = 32
wal_sender_timeout = 20s
hot_standby = on
max_standby_archive_delay = -1
max_standby_streaming_delay = -1
wal_receiver_status_interval = 5s
hot_standby_feedback = on

++ Slave :
wal_level = hot_standby
wal_buffers = 16MB
checkpoint_segments = 32
checkpoint_completion_target = 0.7
archive_mode = on
archive_command = 'cp %p /var/lib/pgsql/9.4/data/archive_log/%f'
max_wal_senders = 3
wal_keep_segments = 32
wal_sender_timeout = 20s
hot_standby = on
max_standby_archive_delay = -1
max_standby_streaming_delay = -1
wal_receiver_status_interval = 5s
hot_standby_feedback = on
-----------------------------------------

Do you have any solution?

Thanks in advance for any help.

Yoji Tsukada.