What is TairHash? - Tair (Redis® OSS-Compatible) - Alibaba Cloud Documentation Center

TairHash (also known as exHash) is an enhanced hash data structure that allows you to specify expiration times and version numbers for fields. TairHash is flexible and can help simplify business development in most scenarios.

Overview

TairHash and Redis Hash support a variety of data interfaces and provide high performance in data processing. However, Redis Hash allows you to specify expiration times only for keys. TairHash allows you to specify expiration times for both keys and fields. You can also use TairHash to specify the version numbers of fields. TairHash is flexible and can help simplify business development in most scenarios. TairHash uses the efficient active expiration algorithm to check the expiration times of fields and delete expired fields. This process does not increase the database response time.

Main features

TairHash allows you to specify expiration times and version numbers for fields.
TairHash supports efficient and flexible expiration policies for fields. The expiration policies can be active or passive.
TairHash provides a similar syntax to Redis Hash.

This module is open-sourced. For more information, see TairHash.

Prerequisites

The instance is of one of the following Tair series types:

DRAM-based instance
Persistent memory-optimized instance whose minor version is 1.2.6 or later

Note

The latest minor version provides more features and higher stability. We recommend that you update your instance to the latest minor version. For more information, see Update the minor version of an instance. If your instance is a cluster or read/write splitting instance, we recommend that you update the proxy nodes in the instance to the latest minor version. This ensures that all commands can be run as expected.

Precautions

The TairHash data that you want to manage is stored on a Tair instance.

Supported commands

Table 1. TairHash commands

Command	Syntax	Description
EXHSET	`EXHSET key field value [EX time] [EXAT time] [PX time] [PXAT time] [NX \| XX] [VER \| ABS version] [KEEPTTL]`	Adds a field to a TairHash key. If the key does not exist, the key is created. If the field already exists, this command overwrites the current value of the field.
EXHGET	`EXHGET key field`	Retrieves the value of a field from a TairHash key. If the key or field does not exist, nil is returned.
EXHMSET	`EXHMSET key field value [field value ...]`	Adds multiple fields to a TairHash key. If the key does not exist, the key is created. If these fields already exist in the key, this command overwrites the values of these fields.
EXHPEXPIREAT	`EXHPEXPIREAT key field milliseconds-timestamp [VER \| ABS version]`	Specifies the absolute expiration time of a field in a TairHash key. Unit: milliseconds.
EXHPEXPIRE	`EXHPEXPIRE key field milliseconds [VER \| ABS version]`	Specifies the relative expiration time of a field in a TairHash key. Unit: milliseconds.
EXHEXPIREAT	`EXHEXPIREAT key field timestamp [VER \| ABS version]`	Specifies the absolute expiration time of a field in a TairHash key. Unit: seconds.
EXHEXPIRE	`EXHEXPIRE key field seconds [VER \| ABS version]`	Specifies the relative expiration time of a field in a TairHash key. Unit: seconds.
EXHPTTL	`EXHPTTL key field`	Queries the TTL of a field in a TairHash key. Unit: milliseconds.
EXHTTL	`EXHTTL key field`	Queries the TTL of a field in a TairHash key. Unit: seconds.
EXHVER	`EXHVER key field`	Queries the current version number of a field in a TairHash key.
EXHSETVER	`EXHSETVER key field version`	Specifies the version number of a field in a TairHash key.
EXHINCRBY	`EXHINCRBY key field num [EX time] [EXAT time] [PX time] [PXAT time] [VER \| ABS version] [MIN minval] [MAX maxval] [KEEPTTL]`	Increases the value of a field in a TairHash key by the num value. The num value must be an integer. If the key does not exist, the key is created. If the field does not exist, this command adds the field and sets the value of the field to 0 before increasing the value of the field. Note To add a field that does not expire, you can run this command to add the field without specifying an expiration time.
EXHINCRBYFLOAT	`EXHINCRBYFLOAT key field num [EX time] [EXAT time] [PX time] [PXAT time] [VER \| ABS version] [MIN minval] [MAX maxval] [KEEPTTL]`	Increases the value of a field in a TairHash key by the num value. The num value must be a floating-point number. If the key does not exist, the key is created. If the field does not exist, this command adds the field and sets the value of the field to 0 before increasing the value of the field. Note To add a field that does not expire, you can run this command to add the field without specifying an expiration time.
EXHGETWITHVER	`EXHGETWITHVER key field`	Retrieves the value and version number of a field from a TairHash key. If the key or field does not exist, nil is returned.
EXHMGET	`EXHMGET key field [field ...]`	Retrieves multiple field values from a TairHash key in each query. If the key does not exist or if the fields do not exist, nil is returned.
EXHMGETWITHVER	`EXHMGETWITHVER key field [field ...]`	Retrieves the values and version numbers of multiple fields from a TairHash key in each query.
EXHLEN	`EXHLEN key [NOEXP]`	Retrieves the number of fields in a TairHash key. The output may include the number of expired fields that are not deleted because this command does not trigger a passive eviction of or filter out expired fields. If you want to retrieve only the number of fields that have not expired, you can set the NOEXP parameter in your command.
EXHEXISTS	`EXHEXISTS key field`	Checks whether a field exists in a TairHash key.
EXHSTRLEN	`EXHSTRLEN key field`	Retrieves the length of a field value from a TairHash key.
EXHKEYS	`EXHKEYS key`	Retrieves all fields from a TairHash key.
EXHVALS	`EXHVALS key`	Retrieves all field values from a TairHash key.
EXHGETALL	`EXHGETALL key`	Retrieves all fields and their values from a TairHash key.
EXHSCAN	`EXHSCAN key op subkey [MATCH pattern] [COUNT count]`	Scans a TairHash key. Note This command is supported only for DRAM-based instances.
EXHSCANUNORDER	`EXHSCANUNORDER key cursor [MATCH pattern] [COUNT count]`	Scans a TairHash key. Note This command is supported only for persistent memory-optimized instances.
EXHDEL	`EXHDEL key field [field ...]`	Deletes a field from a TairHash key. If the key or field does not exist, a value of 0 is returned. If the field is deleted, a value of 1 is returned.
DEL	`DEL <key> [key ...]`	Deletes one or more TairHash keys.

Note

The following list describes the conventions for the command syntax used in this topic:

Uppercase keyword: indicates the command keyword.
Italic text: indicates variables.
[options]: indicates that the enclosed parameters are optional. Parameters that are not enclosed by brackets must be specified.
A|B: indicates that the parameters separated by the vertical bars (|) are mutually exclusive. Only one of the parameters can be specified.
...: indicates that the parameter preceding this symbol can be repeatedly specified.

EXHSET

Item	Description
Syntax	`EXHSET key field value [EX time] [EXAT time] [PX time] [PXAT time] [NX \| XX] [VER \| ABS version] [KEEPTTL]`
Time complexity	O(1)
Command description	Adds a field to a TairHash key. If the key does not exist, the key is created. If the field already exists, this command overwrites the current value of the field. Note To add a field that does not expire, you can run this command to add the field without specifying an expiration time. You can also run the EXPIRE or EXPIREAT command to specify an expiration time for a key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. value: the value of the field. A field can have only a single value. EX: the relative expiration time of the field. Unit: seconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. EXAT: the absolute expiration time of the field. Unit: seconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. PX: the relative expiration time of the field. Unit: milliseconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. PXAT: the absolute expiration time of the field. Unit: milliseconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. NX: specifies that the value is written only if the field does not exist. XX: specifies that the value is written only if the field exists. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists. KEEPTTL: retains the current time-to-live (TTL) of the field if none of the EX, EXAT, PX, and PXAT parameters are specified. Note By default, if the KEEPTTL parameter is not specified, the EXHSET command deletes the current TTL of the field.
Output	If a field is created and a value is set for the field, a value of 1 is returned. If the field already exists and the specified value overwrites the current value of the field, a value of 0 is returned. If the XX parameter is specified and the field does not exist, a value of -1 is returned. If the NX parameter is specified and the field exists, a value of -1 is returned. If the VER parameter is specified and the VER value does not match the current version number, the "ERR update version is stale" message is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHSET myhash field1 val EX 10` Sample output: `(integer) 1`

EXHGET

Item	Description
Syntax	`EXHGET key field`
Time complexity	O(1)
Command description	Retrieves the value of a field from a TairHash key. If the key or field does not exist, nil is returned.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the field exists and the operation is successful, the value of the field is returned. If the key or field does not exist, nil is returned. Otherwise, an error message is returned.
Example	Run the `EXHSET myhash field1 val` command in advance. Sample command: `EXHGET myhash field1` Sample output: `"val"`

EXHMSET

Item	Description
Syntax	`EXHMSET key field value [field value ...]`
Time complexity	O(N)
Command description	Adds multiple fields to a TairHash key. If the key does not exist, the key is created. If these fields already exist in the key, this command overwrites the values of these fields. Note After you create a key, you can run the EXHPEXPIREAT, EXHPEXPIRE, EXHEXPIREAT, or EXHEXPIRE command to specify expiration times for the fields that are added to the key. You can also run the EXPIRE or EXPIREAT command to specify an expiration time for the key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. value: the value of the field. A field can have only a single value.
Output	If the operation is successful, OK is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHMSET myhash field1 val1 field2 val2` Sample output: `OK`

EXHPEXPIREAT

Item	Description
Syntax	`EXHPEXPIREAT key field milliseconds-timestamp [VER \| ABS version]`
Time complexity	O(1)
Command description	Specifies the absolute expiration time of a field in a TairHash key. Unit: milliseconds.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. milliseconds-timestamp: a UNIX timestamp that is accurate to the millisecond. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists.
Output	If the field exists and a value is set for the field, a value of 1 is returned. If the field does not exist, a value of 0 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHPEXPIREAT myhash field1 1293840000` Sample output: `(integer) 1`

EXHPEXPIRE

Item	Description
Syntax	`EXHPEXPIRE key field milliseconds [VER \| ABS version]`
Time complexity	O(1)
Command description	Specifies the relative expiration time of a field in a TairHash key. Unit: milliseconds.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. milliseconds: the relative expiration time. Unit: milliseconds. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists.
Output	If the field exists and a value is set for the field, a value of 1 is returned. If the field does not exist, a value of 0 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHPEXPIRE myhash field1 1000` Sample output: `(integer) 1`

EXHEXPIREAT

Item	Description
Syntax	`EXHEXPIREAT key field timestamp [VER \| ABS version]`
Time complexity	O(1)
Command description	Specifies the absolute expiration time of a field in a TairHash key. Unit: seconds.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. timestamp: a UNIX timestamp that is accurate to the second. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists.
Output	If the field exists and a value is set for the field, a value of 1 is returned. If the field does not exist, a value of 0 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHEXPIREAT myhash field1 1293840000` Sample output: `(integer) 1`

EXHEXPIRE

Item	Description
Syntax	`EXHEXPIRE key field seconds [VER \| ABS version]`
Time complexity	O(1)
Command description	Specifies the relative expiration time of a field in a TairHash key. Unit: seconds.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. seconds: the relative expiration time. Unit: seconds. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists.
Output	If the field exists and a value is set for the field, a value of 1 is returned. If the field does not exist, a value of 0 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHEXPIRE myhash field1 100` Sample output: `(integer) 1`

EXHPTTL

Item	Description
Syntax	`EXHPTTL key field`
Time complexity	O(1)
Command description	Queries the TTL of a field in a TairHash key. Unit: milliseconds.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the field exists and the field does not have a TTL configured, a value of -1 is returned. If the key or field does not exist, a value of -2 is returned. If the field does not exist, a value of -3 is returned. If the field exists and the field has a TTL configured, the TTL is returned. Unit: milliseconds. Otherwise, an error message is returned.
Example	Run the `EXHSET myhash field1 val1 EX 100` command in advance. Sample command: `EXHPTTL myhash field1` Sample output: `(integer) 97213`

EXHTTL

Item	Description
Syntax	`EXHTTL key field`
Time complexity	O(1)
Command description	Queries the TTL of a field in a TairHash key. Unit: seconds.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key or field does not exist, a value of -2 is returned. If the field exists and the field does not have a TTL configured, a value of -1 is returned. If the field exists and the field has a TTL configured, the TTL is returned. Unit: seconds. Otherwise, an error message is returned.
Example	Run the `EXHSET myhash field1 val1 EX 100` command in advance. Sample command: `EXHTTL myhash field1` Sample output: `(integer) 85`

EXHVER

Item	Description
Syntax	`EXHVER key field`
Time complexity	O(1)
Command description	Queries the current version number of a field in a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key does not exist, a value of -1 is returned. If the field does not exist, a value of -2 is returned. If the operation is successful, the version number of the field is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHVER myhash field1` Sample output: `(integer) 1`

EXHSETVER

Item	Description
Syntax	`EXHSETVER key field version`
Time complexity	O(1)
Command description	Specifies the version number of a field in a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key or field does not exist, a value of 0 is returned. If the version number is specified, a value of 1 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHSETVER myhash field1 3` Sample output: `(integer) 1`

EXHINCRBY

Item	Description
Syntax	`EXHINCRBY key field num [EX time] [EXAT time] [PX time] [PXAT time] [VER \| ABS version] [MIN minval] [MAX maxval] [KEEPTTL]`
Time complexity	O(1)
Command description	Increases the value of a field in a TairHash key by the num value. The num value must be an integer. If the key does not exist, the key is created. If the field does not exist, this command adds the field and sets the value of the field to 0 before increasing the value of the field. Note To add a field that does not expire, you can run this command to add the field without specifying an expiration time.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. num: the integer by which you want to increase the value of the field. EX: the relative expiration time of the field. Unit: seconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. EXAT: the absolute expiration time of the field. Unit: seconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. PX: the relative expiration time of the field. Unit: milliseconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. PXAT: the absolute expiration time of the field. Unit: milliseconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists. MIN: the minimum value of the field. If the field value is less than this lower limit, an error message is returned. MAX: the maximum value of the field. If the field value is greater than this upper limit, an error message is returned. KEEPTTL: retains the current TTL of the field if none of the EX, EXAT, PX, and PXAT parameters are specified.
Output	If the operation is successful, the value increased by the num value is returned. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10` command in advance. Sample command: `EXHINCRBY myhash field1 100` Sample output: `(integer) 110`

EXHINCRBYFLOAT

Item	Description
Syntax	`EXHINCRBYFLOAT key field num [EX time] [EXAT time] [PX time] [PXAT time] [VER \| ABS version] [MIN minval] [MAX maxval] [KEEPTTL]`
Time complexity	O(1)
Command description	Increases the value of a field in a TairHash key by the num value. The num value must be a floating-point number. If the key does not exist, the key is created. If the field does not exist, this command adds the field and sets the value of the field to 0 before increasing the value of the field. Note To add a field that does not expire, you can run this command to add the field without specifying an expiration time.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields. num: the floating-point number by which you want to increase the value of the field. EX: the relative expiration time of the field. Unit: seconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. EXAT: the absolute expiration time of the field. Unit: seconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. PX: the relative expiration time of the field. Unit: milliseconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. PXAT: the absolute expiration time of the field. Unit: milliseconds. A value of 0 indicates that the field immediately expires. If this parameter is not specified, the field does not expire. VER: the version number of the field. If the field exists, the version number specified by this parameter is matched against the current version number. If the version numbers match, the system continues to run the command and increases the version number by 1. If the version numbers do not match, an error message is returned. If the field does not exist or the current version number of the field is 0, this parameter is ignored and this command continues to run. After the operation succeeds, the version number is set to 1. ABS: the absolute version number that can be assigned to a field when the field is added, regardless of whether the field already exists. MIN: the minimum value of the field. If the field value is less than this lower limit, an error message is returned. MAX: the maximum value of the field. If the field value is greater than this upper limit, an error message is returned. KEEPTTL: retains the current TTL of the field if none of the EX, EXAT, PX, and PXAT parameters are specified.
Output	If the operation is successful, the value increased by the num value is returned. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10` command in advance. Sample command: `EXHINCRBYFLOAT myhash field1 9.235` Sample output: `"19.235"`

EXHGETWITHVER

Item	Description
Syntax	`EXHGETWITHVER key field`
Time complexity	O(1)
Command description	Retrieves the value and version number of a field from a TairHash key. If the key or field does not exist, nil is returned.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the field exists and the operation is successful, the value and version number of the field are returned. If the key or field does not exist, nil is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHGETWITHVER myhash field1` Sample output: `1) "19.235" 2) (integer) 5`

EXHMGET

Item	Description
Syntax	`EXHMGET key field [field ...]`
Time complexity	O(1)
Command description	Retrieves multiple field values from a TairHash key in each query. If the key does not exist or if the fields do not exist, nil is returned.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key does not exist, nil is returned. If the key and fields exist, an array is returned. Each element in the array corresponds to a field value. If the key exists and specific fields do not exist, an array is returned. Each element in the array corresponds to a field value. The elements that correspond to the fields that do not exist are displayed as nil. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10 field2 var1` command in advance. Sample command: `EXHMGET myhash field1 field2` Sample output: `1) "10" 2) "var1"`

EXHMGETWITHVER

Item	Description
Syntax	`EXHMGETWITHVER key field [field ...]`
Time complexity	O(1)
Command description	Retrieves the values and version numbers of multiple fields from a TairHash key in each query.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key does not exist, nil is returned. If the key and fields exist, an array is returned. Each element in the array corresponds to a field value and a version number. If the key exists and specific fields do not exist, an array is returned. Each element in the array corresponds to a field value and a version number. The elements that correspond to the fields that do not exist are displayed as nil. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10 field2 var1` command in advance. Sample command: `EXHMGETWITHVER myhash field1 field2` Sample output: `1) 1) "10" 2) (integer) 1 2) 1) "var1" 2) (integer) 1`

EXHLEN

Item	Description
Syntax	`EXHLEN key [NOEXP]`
Time complexity	The time complexity is O(1) if the NOEXP parameter is not specified and O(N) if the NOEXP parameter is specified.
Command description	Retrieves the number of fields in a TairHash key. The output may include the number of expired fields that are not deleted because this command does not trigger a passive eviction of or filter out expired fields. If you want to retrieve only the number of fields that have not expired, you can set the NOEXP parameter in your command.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. NOEXP: specifies to return the number of fields that have not expired. By default, this command does not trigger an eviction of or filter out expired fields. For this reason, the output of this command may include the number of expired fields that are not deleted. If you want to retrieve only the number of fields that have not expired, you can set the NOEXP parameter. When you set the NOEXP parameter, take note of the following items: The response time of the EXHLEN command is determined by the size of the key because the system scans all data in the key. The output of the EXHLEN command does not include the number of expired fields because this command filters out expired fields but does not evict them.
Output	If the key does not exist or no fields exist in the key, a value of 0 is returned. If the operation is successful, the number of fields in the key is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHLEN myhash` Sample output: `(integer) 2`

EXHEXISTS

Item	Description
Syntax	`EXHEXISTS key field`
Time complexity	O(1)
Command description	Checks whether a field exists in a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key or field does not exist, a value of 0 is returned. If the field exists, a value of 1 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHEXISTS myhash field1` Sample output: `(integer) 1`

EXHSTRLEN

Item	Description
Syntax	`EXHSTRLEN key field`
Time complexity	O(1)
Command description	Retrieves the length of a field value from a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key or field does not exist, a value of 0 is returned. If the operation is successful, the length of the field value is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHSTRLEN myhash field1` Sample output: `(integer) 2`

EXHKEYS

Item	Description
Syntax	`EXHKEYS key`
Time complexity	O(N)
Command description	Retrieves all fields from a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command.
Output	If the key does not exist, an empty array is returned. If the key exists, an array is returned. Each element in the array corresponds to a field in the key. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10 field2 var1` command in advance. Sample command: `EXHKEYS myhash` Sample output: `1) "field1" 2) "field2"`

EXHVALS

Item	Description
Syntax	`EXHVALS key`
Time complexity	O(N)
Command description	Retrieves all field values from a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command.
Output	If the key does not exist, an empty array is returned. If the key exists, an array is returned. Each element in the array corresponds to a field value in the key. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10 field2 var1` command in advance. Sample command: `EXHVALS myhash` Sample output: `1) "10" 2) "var1"`

EXHGETALL

Item	Description
Syntax	`EXHGETALL key`
Time complexity	O(N)
Command description	Retrieves all fields and their values from a TairHash key.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command.
Output	If the key does not exist, an empty array is returned. If the key exists, an array is returned. Each element in the array corresponds to a field-value pair in the key. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhash field1 10 field2 var1` command in advance. Sample command: `EXHGETALL myhash` Sample output: `1) "field1" 2) "10" 3) "field2" 4) "var1"`

EXHSCAN

Item	Description
Syntax	`EXHSCAN key op subkey [MATCH pattern] [COUNT count]`
Time complexity	The time complexity is O(1) for every call and O(N) for a complete iteration.
Command description	Scans a TairHash key. Note This command is supported only for DRAM-based instances.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. op: the position from which a scan starts. Valid values: >: The scan starts from the first field that has a value greater than the subkey value. >=: The scan starts from the first field that has a value greater than or equal to the subkey value. <: The scan starts from the first field that has a value less than the subkey value. <=: The scan starts from the first field that has a value less than or equal to the subkey value. ==: The scan starts from the first field that has a value equal to the subkey value. ^: The scan starts from the first field. $: The scan starts from the last field. subkey: a parameter that is used together with the op parameter to determine the position from which a scan starts. If the op parameter is set to ^ or $, this parameter is ignored. MATCH: filters the subkeys to be scanned based on a regular expression pattern. COUNT: specifies the number of fields that can be scanned in each query. The default value is 10. Note The COUNT parameter specifies the number of fields scanned in each query and does not ensure that the number of fields returned is the number of fields scanned. The number of fields returned is determined by the number of fields that exist in the key and whether the MATCH parameter is specified.
Output	If the key does not exist, an empty array is returned. If the key exists, an array that contains two elements is returned. The first element is the first field from which the next scan starts. If the key scan is complete, this element is left empty. The second element is the scan result, which includes fields and values. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhashkey field1 val1 field2 val2 field3 val3 field4 val4 field5 val5` command in advance. Sample command: `EXHSCAN myhashkey ^ xx COUNT 3` Sample output: `1) "field4" 2) 1) "field1" 2) "val1" 3) "field2" 4) "val2" 5) "field3" 6) "val3"`

EXHSCANUNORDER

Item	Description
Syntax	`EXHSCANUNORDER key cursor [MATCH pattern] [COUNT count]`
Time complexity	The time complexity is O(1) for every call and O(N) for a complete iteration.
Command description	Scans a TairHash key. Note This command is supported only for persistent memory-optimized instances.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. cursor: the cursor used in this scan. MATCH: filters the fields to be scanned based on a regular expression pattern. COUNT: specifies the number of fields that can be scanned in each query. The default value is 10. Note The COUNT parameter specifies the number of fields scanned in each query and does not ensure that the number of fields returned is the number of fields scanned. The number of fields returned is determined by the number of fields that exist in the key and whether the MATCH parameter is specified.
Output	If the key does not exist, an empty array is returned. If the key exists, an array that contains two elements is returned. The first element of the array is the cursor used for the next scan. If the key scan is complete, a value of 0 is returned. The second element is the scan result, which includes fields and values. Otherwise, an error message is returned.
Example	Run the `EXHMSET myhashkey field1 val1 field2 val2 field3 val3 field4 val4 field5 val5` command in advance. Sample command: `EXHSCANUNORDER myhashkey 0 COUNT 3` Sample output: `1) "1" 2) 1) "field5" 2) "val5" 3) "field2" 4) "val2"`

EXHDEL

Item	Description
Syntax	`EXHDEL key field [field ...]`
Time complexity	O(1)
Command description	Deletes a field from a TairHash key. If the key or field does not exist, a value of 0 is returned. If the field is deleted, a value of 1 is returned.
Parameter	Key: the key that specifies the piece of TairHash data that you want to manage by running this command. field: an element of the key. A key can contain multiple fields.
Output	If the key or field does not exist, a value of 0 is returned. If the operation is successful, a value of 1 is returned. Otherwise, an error message is returned.
Example	Sample command: `EXHDEL myhash field1` Sample output: `(integer) 1`