Limit disk bandwidth to 5MB/s to emulate a slow disk:
echo "8:0 5000000" >
/cgroup/blkio/limit/blkio.throttle.write_bps_device
echo "8:0 5000000" >
/cgroup/blkio/limit/blkio.throttle.read_bps_device
Start scylla node 1 with low memory:
scylla -c 1 -m 128M --auto-bootstrap false
Run c-s:
taskset -c 7 cassandra-stress write duration=5m cl=ONE -schema
'replication(factor=1)' -pop seq=1..100000 -rate threads=20
limit=2000/s -node 127.0.0.1
Start scylla node 2 with low memory:
scylla -c 1 -m 128M --auto-bootstrap true
Without this patch, I saw std::bad_alloc during streaming
ERROR 2016-06-01 14:31:00,196 [shard 0] storage_proxy - exception during
mutation write to 127.0.0.1: std::bad_alloc (std::bad_alloc)
...
ERROR 2016-06-01 14:31:10,172 [shard 0] database - failed to move
memtable to cache: std::bad_alloc (std::bad_alloc)
...
To fix:
1. Apply the streaming mutation limiter before we read the mutation into
memory to avoid wasting memory holding the mutation which we can not
send.
2. Reduce the parallelism of sending streaming mutations. Before we send each
range in parallel, after we send each range one by one.
before: nr_vnode * nr_shard * (send_info + cf.make_reader memory usage)
after: nr_shard * (send_info + cf.make_reader memory usage)
We can at least save memory usage by the factor of nr_vnode, 256 by
default.
In my setup, fix 1) alone is not enough, with both fix 1) and 2), I saw
no std::bad_alloc. Also, I did not see streaming bandwidth dropped due
to 2).
In addition, I tested grow_cluster_test.py:GrowClusterTest.test_grow_3_to_4,
as described:
https://github.com/scylladb/scylla/issues/1270#issuecomment-222585375
With this patch, I saw no std::bad_alloc any more.
Fixes: #1270
Message-Id: <7703cf7a9db40e53a87f0f7b5acbb03fff2daf43.1464785542.git.asias@scylladb.com>
(cherry picked from commit 206955e47c)
c70faa4f23