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What is --connection?

--connection allows you to use predefined connections, that is supported by clickhouse-client (1, 2).

Here is an example in XML format:

<clickhouse>
    <connections_credentials>
        <connection>
            <name>prod</name>
            <hostname>prod</hostname>
            <user>default</user>
            <password>secret</password>
            <!-- <secure>false</secure> -->
            <!-- <skip_verify>false</skip_verify> -->
        </connection>
    </connections_credentials>
</clickhouse>

Or in YAML:

---
connections_credentials:
  prod:
    name: prod
    hostname: prod
    user: default
    password: secret

And later, instead of specifying --url (with password in plain-text, which is highly not recommended), you can use chdig --connection prod.

What are the shortcuts supported?

Category Shortcut Description
Global Shortcuts F1 Show help
F2 Views
F8 Show actions
Ctrl+p Fuzzy actions
F CPU Server Flamegraph
CPU Server Flamegraph in speedscope
~ chdig debug console
q Back/Quit
Esc Back/Quit
Q Quit forcefully
Backspace Back
p Toggle pause
r Refresh
T Seek 10 mins backward
t Seek 10 mins forward
Alt+t Set time interval
Actions Select
- Show all queries
+ Show queries on shards
/ Filter
D Query details
P Query processors
v Query views
C Show CPU flamegraph
R Show Real flamegraph
M Show memory flamegraph
L Show live flamegraph
Show CPU flamegraph in speedscope
Show Real flamegraph in speedscope
Show memory flamegraph in speedscope
Show live flamegraph in speedscope
Alt+E Edit query and execute
s EXPLAIN SYNTAX
e EXPLAIN PLAN
E EXPLAIN PIPELINE
G EXPLAIN PIPELINE graph=1 (open in browser)
I EXPLAIN INDEXES
K KILL query
l Show query Logs
( Increase number of queries to render to 20
) Decrease number of queries to render to 20
Logs j/k down/up
G/g Move to the end/Move to the beginning
PageDown/PageUp Move to the end/Move to the beginning
- Toggle options view (S - toggle wrap mode)
/ Forward search
? Reverse search
n/N Move to next/previous match
Extended Navigation Home reset selection/follow item in table

What is format of the URL accepted by chdig?

Example for secure connection with all default connection settings & user name & password (passing the password in the command line is unsafe)

chdig -u 'user:[email protected]:9440/?secure=true&skip_verify=false&compression=lz4&query_timeout=600s&connection_timeout=5s'

Safer option is to pass the password via the environment variable:

export CLICKHOUSE_USER='user'
export CLICKHOUSE_PASSWORD='password'
chdig -u 'clickhouse-host.com/?secure=true'
# or with port
chdig -u 'clickhouse-host.com:9440/?secure=true'

Or via the configuration file (see above)

Why I see IO wait reported as zero?

  • You should ensure that ClickHouse uses one of taskstat gathering methods:

    • procfs
    • netlink

  • And also for linux 5.14 you should enable kernel.task_delayacct sysctl as well.