added date math for index names

_opensearch/date_math_support.md

@@ -0,0 +1,61 @@
+---
+layout: default
+title: Date math support for index names
+nav_order: 92
+---
+
+# Date math support for index names
+
+Date math is shorthand arithmetic for finding relative dates.
+
+If you're indexing time-series data with the dates mapped in the index names, you can use date math in your queries to filter index names and limit the number of searched indices.
+
+## Date math syntax
+
+The date math syntax for an index name is as follows:
+
+```
+<static_name{date_math_expr{date_format|time_zone}}>
+```
+
+where:
+
+- `static_name` is the unchanged or static portion of the index name. To use the characters `{` and `}` in the static part of an index name, escape them with a backslash `\`.
+- `date_math_expr`: The changing or dynamic portion of the index name that’s computed by the date math expression. For example, `now+1h` adds one hour, `now-1d` subtracts one hour, and `now/d` rounds down to the nearest day, where `now` represents the current timestamp.
+- `date_format`: (Optional) Specify the format for the computed date. The default value is `YYYY.MM.dd`. Make sure that you’re using the correct small or capital letters in the date format. For example, `mm` denotes minute of hour, while `MM` denotes month of year. Similarly, `hh` denotes the hour in the `1-12` range in combination with AM/PM, while `HH` denotes the hour in the `0-23` 24-hour range.
+- `time_zone`: (Optional) Specify the timezone offset. The default value is UTC. For example, the UTC time offset for PST is `-08:00`.
+
+## Date math example
+
+You must enclose date math index names within angle brackets.
+
+If today is 22nd March, 2024:
+
+- `<logstash-{now/d}>` resolves to `logstash-2024.03.22`
+- `<logstash-{now/M}>` resolves to `logstash-2024.03.01`
+- `<logstash-{now/M{YYYY.MM}}>` resolves to `logstash-2024.03`
+- `<logstash-{now/M-1M{YYYY.MM}}>` resolves to `logstash-2024.02`
+- `<logstash-{now/d{yyyy.MM.dd|+12:00}}>` resolves to `logstash-2024.03.23`
+
+You need to encode all special characters in URI format:
+
+Special characters | URI format
+:--- | :---
+`<` | %3C
+`>` | %3E
+`/` | %2F
+`{` | %7B
+`}` | %7D
+`|` | %7C
+`+` | %2B
+`:` | %3A
+`,` | %2C
+
+If you are searching for errors in your daily logs with the default Logstash index name format `logstash-YYYY.MM.dd`, you can use date math to restrict the search to indices of the past three days:
+
+```
+# GET <logstash-{now/d-2d}>,<logstash-{now/d-1d}>,<logstash-{now/d}>/_search
+GET %3Clogstash-%7Bnow%2Fd-2d%7D%3E%2C%3Clogstash-%7Bnow%2Fd-1d%7D%3E%2C%3Clogstash-%7Bnow%2Fd%7D%3E/_search
+```
+
+This date math expression is evaluated at runtime.