Q:

Redis, reading while writing with NodeJS

I have a NodeJS worker that updates my Redis database every hour. The work queries a remote database in batches so that groups of requests are sent in series, so as to maximize performance (on the remote database).
When I write the responses back to my Redis Sorted Set(s), I observe that - on occasion -  reading from the Redis database gets very slow, and performs as if there is blocking taking place.
I have tried my very best to ascertain why this only happens on occasion, but I cannot replicate performance reliably, nor in any systematic way.
Is there any good reason why performance would degrade so much? Am I missing something?
Redis on Window:
redis_version:2.4.6
redis_git_sha1:26cdd13a
redis_git_dirty:0
arch_bits:64
multiplexing_api:winsock2
gcc_version:4.6.1
process_id:7512
uptime_in_seconds:202034
uptime_in_days:2
lru_clock:23886
used_cpu_sys:290.65
used_cpu_user:2261.94
used_cpu_sys_children:0.00
used_cpu_user_children:0.00
connected_clients:3
connected_slaves:0
client_longest_output_list:0
client_biggest_input_buf:0
blocked_clients:0
used_memory:780833728
used_memory_human:744.66M
used_memory_rss:780833728
used_memory_peak:780849896
used_memory_peak_human:744.68M
mem_fragmentation_ratio:1.00
mem_allocator:libc
loading:0
aof_enabled:0
changes_since_last_save:-26
bgsave_in_progress:0
last_save_time:1384359002
bgrewriteaof_in_progress:0
total_connections_received:6
total_commands_processed:12908729
expired_keys:0
evicted_keys:0
keyspace_hits:12907834
keyspace_misses:888
pubsub_channels:0
pubsub_patterns:0
latest_fork_usec:0
vm_enabled:0
role:master
db0:keys=698,expires=0

A:

It would seem as though the comment by zenbeni was pretty accurate. Redis will dump to disk upon a certain number of updates, if left in the default mode. However, in my use case, in reality this is pretty much random as there isn't really anything systematic regarding how many updates are generated after each external query. 
Accordingly, when Redis is dumping to hard disk and it also reading and writing to the database in memory, things slow down. It's not clear to me at this stage whether this is a particular problem to the Windows version of Redis that I have had to use. I would imagine that once I get into a more mature version of the product, I'll be able to move over to linux based OS.

