Here is the relevant part of the config:
<remote_servers>
<bad>
<shard>
<replica>
<host>127.0.0.2</host>
<port>2</port>
</replica>
</shard>
</bad>
</remote_servers> (I also turned off listening on 0.0.0.0 and ::)
So we have the "bad" cluster:
:) SELECT * FROM system.clusters
SELECT *
FROM system.clusters
┌─cluster─┬─shard_num─┬─shard_weight─┬─replica_num─┬─host_name─┬─host_address─┬─port─┬─is_local─┬─user────┬─default_database─┐
│ bad │ 1 │ 1 │ 1 │ 127.0.0.2 │ 127.0.0.2 │ 2 │ 0 │ default │ │
└─────────┴───────────┴──────────────┴─────────────┴───────────┴──────────────┴──────┴──────────┴─────────┴──────────────────┘
1 rows in set. Elapsed: 8.030 sec.
With default settings Clickhouse will try accessing this cluster 3 times:
:) SELECT hostName() FROM remote("bad", default.tmp)
SELECT hostName()
FROM remote(bad, default.tmp)
Received exception from server (version 19.1.6):
Code: 279. DB::Exception: Received from click:9000, 172.19.0.18. DB::NetException. DB::NetException: All connection tries failed. Log:
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
.
0 rows in set. Elapsed: 0.003 sec.Same thing happens if we will specify address(es) manually:
:) SELECT hostName() FROM remote('127.0.0.2', default.tmp)
SELECT hostName()
FROM remote('127.0.0.2', default.tmp)
Received exception from server (version 19.1.6):
Code: 279. DB::Exception: Received from click:9000, 172.19.0.18. DB::NetException. DB::NetException: All connection tries failed. Log:
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
.
0 rows in set. Elapsed: 0.003 sec.Let's change this setting:
:) SET connections_with_failover_max_tries = 5
SET connections_with_failover_max_tries = 5
Ok.
0 rows in set. Elapsed: 0.001 sec.
So now, in previous example we will have 5 attempts:
:) SELECT hostName() FROM remote('127.0.0.2', default.tmp)
SELECT hostName()
FROM remote('127.0.0.2', default.tmp)
Received exception from server (version 19.1.6):
Code: 279. DB::Exception: Received from click:9000, 172.19.0.18. DB::NetException. DB::NetException: All connection tries failed. Log:
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:9000), e.what() = DB::NetException
.
0 rows in set. Elapsed: 0.003 sec.(note 5 Code: 210 lines)
But with cluster these (and some other) settings are ignored:
:) SELECT hostName() FROM remote("bad", default.tmp)
SELECT hostName()
FROM remote(bad, default.tmp)
Received exception from server (version 19.1.6):
Code: 279. DB::Exception: Received from click:9000, 172.19.0.18. DB::NetException. DB::NetException: All connection tries failed. Log:
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
.
0 rows in set. Elapsed: 0.003 sec.Specifying settings in query doesn't help:
:) SELECT hostName() FROM remote("bad", default.tmp) SETTINGS connections_with_failover_max_tries = 5
SELECT hostName()
FROM remote(bad, default.tmp)
SETTINGS connections_with_failover_max_tries = 5
Received exception from server (version 19.1.6):
Code: 279. DB::Exception: Received from click:9000, 172.19.0.18. DB::NetException. DB::NetException: All connection tries failed. Log:
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
Code: 210, e.displayText() = DB::NetException: Connection refused (127.0.0.2:2), e.what() = DB::NetException
.
0 rows in set. Elapsed: 0.003 sec. This is reproducible in at least 5 or 6 latest -stable versions, something similar was first noticed in November 2017.
Consequences of this is that ENGINE=Distributed tables do not work and cannot be forced to work across multiple data centers in different parts of the world.
Here is the relevant part of the config:
(I also turned off listening on
0.0.0.0and::)So we have the "bad" cluster:
With default settings Clickhouse will try accessing this cluster 3 times:
Same thing happens if we will specify address(es) manually:
Let's change this setting:
So now, in previous example we will have 5 attempts:
(note 5
Code: 210lines)But with cluster these (and some other) settings are ignored:
Specifying settings in query doesn't help:
This is reproducible in at least 5 or 6 latest -stable versions, something similar was first noticed in November 2017.
Consequences of this is that
ENGINE=Distributedtables do not work and cannot be forced to work across multiple data centers in different parts of the world.