*) Problem:
We have seen in the field it takes longer than expected to repair system tables
like system_auth which has a tiny amount of data but is replicated to all nodes
in the cluster. The cluster has multiple DCs. Each DC has multiple nodes. The
main reason for the slowness is that even if the amount of data is small,
repair has to walk though all the token ranges, that is num_tokens *
number_of_nodes_in_the_cluster. The overhead of the repair protocol for each
token range dominates due to the small amount of data per token range. Another
reason is the high network latency between DCs makes the RPC calls used to
repair consume more time.
*) Solution:
To solve this problem, a small table optimization for repair is introduced in
this patch. A new repair option is added to turn on this optimization.
- No token range to repair is needed by the user. It will repair all token
ranges automatically.
- Users only need to send the repair rest api to one of the nodes in the
cluster. It can be any of the nodes in the cluster.
- It does not require the RF to be configured to replicate to all nodes in the
cluster. This means it can work with any tables as long as the amount of data
is low, e.g., less than 100MiB per node.
*) Performance:
1)
3 DCs, each DC has 2 nodes, 6 nodes in the cluster. RF = {dc1: 2, dc2: 2, dc3: 2}
Before:
```
repair - repair[744cd573-2621-45e4-9b27-00634963d0bd]: stats:
repair_reason=repair, keyspace=system_auth, tables={roles, role_attributes,
role_members}, ranges_nr=1537, round_nr=4612,
round_nr_fast_path_already_synced=4611,
round_nr_fast_path_same_combined_hashes=0, round_nr_slow_path=1,
rpc_call_nr=115289, tx_hashes_nr=0, rx_hashes_nr=5, duration=1.5648403 seconds,
tx_row_nr=2, rx_row_nr=0, tx_row_bytes=356, rx_row_bytes=0,
row_from_disk_bytes={{127.0.14.1, 178}, {127.0.14.2, 178}, {127.0.14.3, 0},
{127.0.14.4, 0}, {127.0.14.5, 178}, {127.0.14.6, 178}},
row_from_disk_nr={{127.0.14.1, 1}, {127.0.14.2, 1}, {127.0.14.3, 0},
{127.0.14.4, 0}, {127.0.14.5, 1}, {127.0.14.6, 1}},
row_from_disk_bytes_per_sec={{127.0.14.1, 0.00010848}, {127.0.14.2,
0.00010848}, {127.0.14.3, 0}, {127.0.14.4, 0}, {127.0.14.5, 0.00010848},
{127.0.14.6, 0.00010848}} MiB/s, row_from_disk_rows_per_sec={{127.0.14.1,
0.639043}, {127.0.14.2, 0.639043}, {127.0.14.3, 0}, {127.0.14.4, 0},
{127.0.14.5, 0.639043}, {127.0.14.6, 0.639043}} Rows/s,
tx_row_nr_peer={{127.0.14.3, 1}, {127.0.14.4, 1}}, rx_row_nr_peer={}
```
After:
```
repair - repair[d6e544ba-cb68-4465-ab91-6980bcbb46a9]: stats:
repair_reason=repair, keyspace=system_auth, tables={roles, role_attributes,
role_members}, ranges_nr=1, round_nr=4, round_nr_fast_path_already_synced=4,
round_nr_fast_path_same_combined_hashes=0, round_nr_slow_path=0,
rpc_call_nr=80, tx_hashes_nr=0, rx_hashes_nr=0, duration=0.001459798 seconds,
tx_row_nr=0, rx_row_nr=0, tx_row_bytes=0, rx_row_bytes=0,
row_from_disk_bytes={{127.0.14.1, 178}, {127.0.14.2, 178}, {127.0.14.3, 178},
{127.0.14.4, 178}, {127.0.14.5, 178}, {127.0.14.6, 178}},
row_from_disk_nr={{127.0.14.1, 1}, {127.0.14.2, 1}, {127.0.14.3, 1},
{127.0.14.4, 1}, {127.0.14.5, 1}, {127.0.14.6, 1}},
row_from_disk_bytes_per_sec={{127.0.14.1, 0.116286}, {127.0.14.2, 0.116286},
{127.0.14.3, 0.116286}, {127.0.14.4, 0.116286}, {127.0.14.5, 0.116286},
{127.0.14.6, 0.116286}} MiB/s, row_from_disk_rows_per_sec={{127.0.14.1,
685.026}, {127.0.14.2, 685.026}, {127.0.14.3, 685.026}, {127.0.14.4, 685.026},
{127.0.14.5, 685.026}, {127.0.14.6, 685.026}} Rows/s, tx_row_nr_peer={},
rx_row_nr_peer={}
```
The time to finish repair difference = 1.5648403 seconds / 0.001459798 seconds = 1072X
2)
3 DCs, each DC has 2 nodes, 6 nodes in the cluster. RF = {dc1: 2, dc2: 2, dc3: 2}
Same test as above except 5ms delay is added to simulate multiple dc
network latency:
The time to repair is reduced from 333s to 0.2s.
333.26758 s / 0.22625381s = 1472.98
3)
3 DCs, each DC has 3 nodes, 9 nodes in the cluster. RF = {dc1: 3, dc2: 3, dc3: 3}
, 10 ms network latency
Before:
```
repair - repair[86124a4a-fd26-42ea-a078-437ca9e372df]: stats:
repair_reason=repair, keyspace=system_auth, tables={role_attributes,
role_members, roles}, ranges_nr=2305, round_nr=6916,
round_nr_fast_path_already_synced=6915,
round_nr_fast_path_same_combined_hashes=0, round_nr_slow_path=1,
rpc_call_nr=276630, tx_hashes_nr=0, rx_hashes_nr=8, duration=986.34015
seconds, tx_row_nr=7, rx_row_nr=0, tx_row_bytes=1246, rx_row_bytes=0,
row_from_disk_bytes={{127.0.57.1, 178}, {127.0.57.2, 178}, {127.0.57.3,
0}, {127.0.57.4, 0}, {127.0.57.5, 0}, {127.0.57.6, 0}, {127.0.57.7, 0},
{127.0.57.8, 0}, {127.0.57.9, 0}}, row_from_disk_nr={{127.0.57.1, 1},
{127.0.57.2, 1}, {127.0.57.3, 0}, {127.0.57.4, 0}, {127.0.57.5, 0},
{127.0.57.6, 0}, {127.0.57.7, 0}, {127.0.57.8, 0}, {127.0.57.9, 0}},
row_from_disk_bytes_per_sec={{127.0.57.1, 1.72105e-07}, {127.0.57.2,
1.72105e-07}, {127.0.57.3, 0}, {127.0.57.4, 0}, {127.0.57.5, 0},
{127.0.57.6, 0}, {127.0.57.7, 0}, {127.0.57.8, 0}, {127.0.57.9, 0}}
MiB/s, row_from_disk_rows_per_sec={{127.0.57.1, 0.00101385},
{127.0.57.2, 0.00101385}, {127.0.57.3, 0}, {127.0.57.4, 0},
{127.0.57.5, 0}, {127.0.57.6, 0}, {127.0.57.7, 0}, {127.0.57.8, 0},
{127.0.57.9, 0}} Rows/s, tx_row_nr_peer={{127.0.57.3, 1},
{127.0.57.4, 1}, {127.0.57.5, 1}, {127.0.57.6, 1}, {127.0.57.7, 1},
{127.0.57.8, 1}, {127.0.57.9, 1}}, rx_row_nr_peer={}
```
After:
```
repair - repair[07ebd571-63cb-4ef6-9465-6e5f1e98f04f]: stats:
repair_reason=repair, keyspace=system_auth, tables={role_attributes,
role_members, roles}, ranges_nr=1, round_nr=4,
round_nr_fast_path_already_synced=4,
round_nr_fast_path_same_combined_hashes=0, round_nr_slow_path=0,
rpc_call_nr=128, tx_hashes_nr=0, rx_hashes_nr=0, duration=1.6052915
seconds, tx_row_nr=0, rx_row_nr=0, tx_row_bytes=0, rx_row_bytes=0,
row_from_disk_bytes={{127.0.57.1, 178}, {127.0.57.2, 178}, {127.0.57.3,
178}, {127.0.57.4, 178}, {127.0.57.5, 178}, {127.0.57.6, 178},
{127.0.57.7, 178}, {127.0.57.8, 178}, {127.0.57.9, 178}},
row_from_disk_nr={{127.0.57.1, 1}, {127.0.57.2, 1}, {127.0.57.3, 1},
{127.0.57.4, 1}, {127.0.57.5, 1}, {127.0.57.6, 1}, {127.0.57.7, 1},
{127.0.57.8, 1}, {127.0.57.9, 1}},
row_from_disk_bytes_per_sec={{127.0.57.1, 0.00037793}, {127.0.57.2,
0.00037793}, {127.0.57.3, 0.00037793}, {127.0.57.4, 0.00037793},
{127.0.57.5, 0.00037793}, {127.0.57.6, 0.00037793}, {127.0.57.7,
0.00037793}, {127.0.57.8, 0.00037793}, {127.0.57.9, 0.00037793}}
MiB/s, row_from_disk_rows_per_sec={{127.0.57.1, 2.22634},
{127.0.57.2, 2.22634}, {127.0.57.3, 2.22634}, {127.0.57.4,
2.22634}, {127.0.57.5, 2.22634}, {127.0.57.6, 2.22634},
{127.0.57.7, 2.22634}, {127.0.57.8, 2.22634}, {127.0.57.9,
2.22634}} Rows/s, tx_row_nr_peer={}, rx_row_nr_peer={}
```
The time to repair is reduced from 986s (16 minutes) to 1.6s
*) Summary
So, a more than 1000X difference is observed for this common usage of
system table repair procedure.
Fixes#16011
Refs #15159
c605220bb3