Tair (Redis® OSS-Compatible):exHash

Overview

TairHash extends the standard Redis hash with two capabilities that native Redis hash lacks: per-field expiration and per-field versioning. You can set a TTL on individual fields without affecting the rest of the key, and use version numbers to prevent conflicting concurrent writes.

TairHash uses an Active Expire algorithm that proactively checks and deletes expired fields without noticeably affecting response time. It also supports passive expiration, which removes expired fields on access.

Key features

• Set an expiration time and version for each field.

• Use active and passive expiration policies for fields.

• Use syntax similar to the native Redis hash data type.

This module is open source. For more information, see TairHash.

Prerequisites

Before you begin, ensure you have:

• A Tair instance of one of the following types:

  • Memory-optimized

  • Persistent memory-optimized (minor version 1.2.6 or later)

Keep your instance on the latest minor version for additional features and improved stability. See Minor version update. For instances using a cluster architecture or read/write splitting architecture, also update the proxy nodes — otherwise some commands may not be recognized.

Precautions

The commands operate on TairHash data in a Tair instance.

Commands

The following tables list all TairHash commands, grouped by operation type.

EXHSET

Options

After you set a timeout for a field, running EXHSET again without a timeout option clears the expiration (unless you use KEEPTTL). To set an expiration on the key itself, use the native EXPIRE or EXPIREAT command.

Return values

Example

EXHSET myhash field1 val EX 10

(integer) 1

EXHGET

Return values

Example

EXHSET myhash field1 val
EXHGET myhash field1

"val"

EXHMSET

To set expiration on individual fields after creation, use EXHEXPIRE, EXHPEXPIRE, EXHEXPIREAT, or EXHPEXPIREAT. To set expiration on the key itself, use the native EXPIRE or EXPIREAT command.

Return values

Example

EXHMSET myhash field1 val1 field2 val2

OK

EXHEXPIRE

Options

Return values

Example

EXHSET myhash field1 val
EXHEXPIRE myhash field1 100

(integer) 1

EXHPEXPIRE

Options

Return values

Example

EXHSET myhash field1 val
EXHPEXPIRE myhash field1 1000

(integer) 1

EXHEXPIREAT

Options

Return values

Example

EXHEXPIREAT myhash field1 1293840000

(integer) 1

EXHPEXPIREAT

Options

Return values

Example

EXHPEXPIREAT myhash field1 1293840000000

(integer) 1

EXHTTL

Return values

Example

The following example shows all possible return states in a single sequence: a field with a TTL set (85), and a field with no expiration (-1).

EXHSET myhash field1 val1 EX 100
EXHSET myhash field2 val2
EXHTTL myhash field1
EXHTTL myhash field2
EXHTTL myhash field3

(integer) 85
(integer) -1
(integer) -3

EXHPTTL

Return values

Example

EXHSET myhash field1 val1 EX 100
EXHPTTL myhash field1

(integer) 97213

EXHVER

Return values

Example

EXHVER myhash field1

(integer) 1

EXHSETVER

Return values

Example

EXHSETVER myhash field1 3

(integer) 1

EXHINCRBY

Options

After you set a timeout for a field, running EXHINCRBY again without a timeout option clears the expiration (unless you use KEEPTTL).

Return values

Example

EXHMSET myhash field1 10
EXHINCRBY myhash field1 100

(integer) 110

EXHINCRBYFLOAT

Options

After you set a timeout for a field, running EXHINCRBYFLOAT again without a timeout option clears the expiration (unless you use KEEPTTL).

Return values

Example

EXHMSET myhash field1 10
EXHINCRBYFLOAT myhash field1 9.235

"19.235"

EXHGETWITHVER

Return values

Example

EXHGETWITHVER myhash field1

1) "19.235"
2) (integer) 5

EXHMGET

Return values

Example

EXHMSET myhash field1 10 field2 var1
EXHMGET myhash field1 field2

1) "10"
2) "var1"

EXHMGETWITHVER

Return values

Example

EXHMSET myhash field1 10 field2 var1
EXHMGETWITHVER myhash field1 field2

1) 1) "10"
   2) (integer) 1
2) 1) "var1"
   2) (integer) 1

EXHLEN

Options

Return values

Example

EXHLEN myhash

(integer) 2

EXHEXISTS

Return values

Example

EXHEXISTS myhash field1

(integer) 1

EXHSTRLEN

Return values

Example

EXHSTRLEN myhash field1

(integer) 2

EXHKEYS

Return values

Example

EXHMSET myhash field1 10 field2 var1
EXHKEYS myhash

1) "field1"
2) "field2"

EXHVALS

Return values

Example

EXHMSET myhash field1 10 field2 var1
EXHVALS myhash

1) "10"
2) "var1"

EXHGETALL

Return values

Example

EXHMSET myhash field1 10 field2 var1
EXHGETALL myhash

1) "field1"
2) "10"
3) "field2"
4) "var1"

EXHSCAN

Options

Valid `op` values

Return values

The response is an array of two elements:

1. The starting field for the next scan call. Empty when the scan is complete.

2. The scanned fields and their values, interleaved as [field, value, field, value, ...].

Returns an empty array if the key does not exist.

Example

EXHMSET myhashkey field1 val1 field2 val2 field3 val3 field4 val4 field5 val5
EXHSCAN myhashkey ^ xx COUNT 3

1) "field4"
2) 1) "field1"
   2) "val1"
   3) "field2"
   4) "val2"
   5) "field3"
   6) "val3"

The next scan starts from field4. Pass field4 as subkey with op >= to continue.

EXHDEL

Return values

Example

EXHDEL myhash field1

(integer) 1

FAQ

Why does exHash use more memory than a standard Redis hash for the same data?

Each field in TairHash stores additional metadata — the expiration timestamp and version number — that a standard Redis hash does not have. This extra per-field metadata is the source of the higher memory usage.