Scheduling a snapshot - Amazon Redshift
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Scheduling a snapshot

To precisely control when to take a snapshot, you can create a snapshot schedule for specific namepsaces. When scheduling snapshot creation, you can create either a one-time event or use Unix cron expressions to create a recurring schedule. Cron expressions support three fields and are separated by white space.

cron(Minutes Hours Day-of-month Month Day-of-week Year)
Fields Values Wildcards

Minutes

0–59

, - * /

Hours

0–23

, - * /

Day-of-month

1–31

, - * ? / L W

Month

1–12 or JAN-DEC

, - * /

Day-of-week

1–7 or SUN-SAT

, - * ? L #

Year

1970–2199

, - * /
Wildcards

  • The , (comma) wildcard includes additional values. In the Day-of-week field, MON,WED,FRI would include Monday, Wednesday, and Friday. Total values are limited to 24 per field.

  • The - (dash) wildcard specifies ranges. In the Hour field, 1–15 would include hours 1 through 15 of the specified day.

  • The * (asterisk) wildcard includes all values in the field. In the Hours field, * would include every hour.

  • The / (forward slash) wildcard specifies increments. In the Hours field, you could enter 1/10 to specify every 10th hour, starting from the first hour of the day (for example, the 01:00, 11:00, and 21:00).

  • The ? (question mark) wildcard specifies one or another. In the Day-of-month field you could enter 7, and if you didn't care what day of the week the seventh was, you could enter ? in the Day-of-week field.

  • The L wildcard in the Day-of-month or Day-of-week fields specifies the last day of the month or week.

  • The W wildcard in the Day-of-month field specifies a weekday. In the Day-of-month field, 3W specifies the day closest to the third weekday of the month.

  • The # wildcard in the Day-of-week field specifies a certain instance of the specified day of the week within a month. For example, 3#2 would be the second Tuesday of the month: the 3 refers to Tuesday because it is the third day of each week, and the 2 refers to the second day of that type within the month.

    Note

    If you use a '#' character, you can define only one expression in the day-of-week field. For example, "3#1,6#3" is not valid because it is interpreted as two expressions.

Limits

  • You can't specify the Day-of-month and Day-of-week fields in the same cron expression. If you specify a value in one of the fields, you must use a ? (question mark) in the other.

  • Snapshot schedules don't support the following frequencies:

    • Snapshots scheduled more frequently than 1 per hour.

    • Snapshots scheduled less frequently than 1 per day (24 hours).

    If you have overlapping schedules that result in scheduling snapshots within a 1 hour window, a validation error results.

The following table has some sample cron strings.

Minutes Hours Day of week Meaning

0

14-20/1

TUE

Every hour between 2pm and 8pm on Tuesday.

0

21

MON-FRI

Every night at 9pm Monday–Friday.

30

0/6

SAT-SUN

Every 6 hour increment on Saturday and Sunday starting at 30 minutes after midnight (00:30) that day. This results in a snapshot at [00:30, 06:30, 12:30, and 18:30] each day.

30

12/4

*

Every 4 hour increment starting at 12:30 each day. This resolves to [12:30, 16:30, 20:30].

The following example demonstrates how to create a schedule that runs in 2-hour increments starting at 15:15 each day.

 cron(15 15/2 *)

Currently, you can only use the Amazon Redshift Serverless API or Amazon CLI to create a snapshot schedule. For more information about those operations, see Using the Amazon CLI and Amazon Redshift Serverless API.