By default, MemSQL uses the time zone setting on the host (the Linux OS). You can update the time zone on the host or through MemSQL via the default_time_zone configuration option.
We recommend that you set the time zone on the host instead of setting the MemSQL default_time_zone
configuration option, when possible. Also, when you use either of these two methods, we recommend that you set the time zone to UTC and then have your application convert UTC time to the user’s local time zone.
Setting the Time Zone on the Host (Linux OS)
If you are setting the time zone on the host (the Linux OS), then you must set the time zone to the same value on every host in your cluster.
Note: It is recommended to execute the commands first on a development or a test cluster.
The following are the steps to set the time zone on RHEL OS:
-
Shutdown the MemSQL cluster.
-
Execute the following commands on each node of the cluster:
timedatectl status timedatectl set-timezone Europe/London timedatectl status
Note: “Europe/London” is used as an example in the code block above; however, you can set the time zone to any other location as well.
-
Start the MemSQL cluster.
Setting the Time Zone in MemSQL
The default_time_zone
configuration option can be used to set the time zone by specifying an offset from UTC time. While updating a time zone on a host, it is required to set it identically on all hosts in the MemSQL cluster and then restart the cluster. For example, to set the time zone to UTC on a host, run the command:
memsql-admin update-config --key default_time_zone --value "+00:00" --all
And then restart the cluster by running the following command:
memsql-admin restart-node --all
For example, to specify an offset of 01 hour from UTC, run the following command and restart the cluster.
memsql-admin update-config --key default_time_zone --value "+01:00" --all
Note: default_time_zone
is a startup configuration option and not engine variable, so you cannot read or write it using the SELECT
or SET
command.
When you set default_time_zone
(for example to the value UTC
), then the time_zone variable is set to the same value as default_time_zone
.
SELECT @@TIME_ZONE;
****
+-------------+
| @@TIME_ZONE |
+-------------+
| UTC |
+-------------+
The actual time zone used by MemSQL is time_zone
(which is set in default_time_zone
). So, the CURRENT_TIMESTAMP()
or LOCALTIMESTAMP()
displays the actual time zone used by MemSQL:
SELECT CURRENT_TIMESTAMP();
****
+---------------------+
| CURRENT_TIMESTAMP() |
+---------------------+
| 2020-05-26 11:27:56 |
+---------------------+
When you query DATETIME
values, MemSQL displays the timestamp according to the default_time_zone
setting.
For example, assume that the default_time_zone
is set to -4:00
and you insert a DATETIME
value 2020-07-08 15:40:52
. Now, you set the default_time_zone
to -7:00
and then query the same DATETIME
value. You will notice that the value is now 2020-07-08 12:40:52
. The queried value differs from the inserted value by the same difference between the current and previous default_time_zone
values.
Time Zone Engine Variables
system_time_zone
variable
This variable stores the time zone set on the host (the Linux OS). It is a read-only variable and read by the engine during startup.
SELECT @@SYSTEM_TIME_ZONE;
****
+--------------------+
| @@SYSTEM_TIME_ZONE |
+--------------------+
| UTC |
+--------------------+
time_zone
variable
This variable exists in MemSQL only to conform to MySQL standards. Setting this variable does not do anything. If MemSQL is using the time zone setting of the host (the Linux OS), then the time_zone
variable returns the value SYSTEM
. If you set the time zone through MemSQL, via the default_time_zone configuration option, then the time_zone
variable returns the value of default_time_zone
.
SELECT @@TIME_ZONE;
****
+-------------+
| @@TIME_ZONE |
+-------------+
| SYSTEM |
+-------------+