How to use scan command in Redis

The SCAN command allows iterating over Redis key-value pairs. It uses cursors to track progress, supports pattern matching and specifies the number of key-value pairs returned per iteration. Iterating is started with SCAN 0, and the subsequent calls use the cursor that was returned last time. This command returns a cursor and an array containing the retrieved key-value pairs. SCAN is non-blocking and returns up to 1000 key-value pairs per iteration. Complete iteration needs to stop when the cursor becomes 0.

Use of SCAN commands in Redis

Overview

The SCAN command is used to iterate over key-value pairs in the Redis database. It provides an efficient and scalable way to traverse large datasets.

grammar

 <code>SCAN cursor [MATCH pattern] [COUNT count]</code>

Parameter description

• cursor: Cursor used to track iteration progress. The initial value should be 0.
• MATCH pattern: The pattern used to match the key to be retrieved.
• COUNT count: Specifies the number of key-value pairs to be returned in each iteration.

usage

When using the SCAN command, you need to specify a cursor as the starting point. The cursor should be 0 for the first call. Subsequent calls should use the cursor returned by the last call.

This command returns an array containing two elements:

• Cursor: Updated cursor used to continue iteration.
• Value: an array containing key-value pairs retrieved in each iteration.

Example

 <code># 迭代所有键值对SCAN 0 # 迭代以"foo" 开头的键SCAN 0 MATCH foo* # 每次迭代返回10 个键值对SCAN 0 COUNT 10</code>

Things to note

• The SCAN command is non-blocking, which means it does not prevent the server from performing other operations.
• The SCAN command returns up to 1000 key-value pairs per iteration. Use the COUNT parameter to control the number of key-value pairs returned per iteration.
• To complete the iteration, you need to stop when the cursor is 0.

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