Redis Programming Tutorials: Learn Redis Online-php.cn

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Technical Articles

Database

Redis

How to get all fields and values from a hash using HGETALL?

HGETALL returns all fields and values in the hash table, and the results are presented in a flat list of alternating field values. For example: executing HGETALLuser:1 will return field value pairs such as "name", "Alice", "age", and "30" in turn. When using different clients, most libraries such as Python's redis-py, Node.js' ioredis, etc. will automatically convert the results into dictionaries or objects; if manually parsed, they need to be paired in order. Alternatives should be considered when facing large hashes, including using HSCAN paging to obtain, locally cache stable data, or splitting

Aug 06, 2025 am 04:29 AM

What is a Redis Sorted Set (ZSET) and how does it differ from a regular Set?

ARedisSortedSet(ZSET)isadatastructurethatstoresuniqueelements,eachassociatedwithascoretomaintainasortedorder.1.Elementsaresortedbytheirfloating-pointscoresinascendingorder.2.Membersareunique,butmultiplememberscanhavethesamescore,leadingtolexicographi

Aug 06, 2025 am 03:32 AM

How Can I Install Redis on a Linux System from Source?

InstallingRedisonLinuxfromsourceisbeneficialforaccessingthelatestfeaturesandunderstandingitsoperations.Stepsinclude:1)Installnecessarytoolswithsudoapt-getupdateandsudoapt-getinstallbuild-essential;2)DownloadthelatestRedisreleaseusingwgethttps://downl

Aug 06, 2025 am 02:00 AM

What are some practical applications of Redis Geospatial indexes?

Redis's geospatial index can be used in a variety of real-time location query scenarios. 1. Find nearby points of interest, such as using GEOADD to add locations and using GEORADIUS to quickly obtain coffee shops within a specified radius; 2. Real-time friend/follower location tracking, suitable for displaying nearby users in social or shared applications; 3. Optimize delivery or logistics routes, and achieve rapid task allocation by storing driver locations; 4. Lightweight geofence function, combined with periodic distance inspection to achieve area triggering operations without complex facilities.

Aug 06, 2025 am 01:40 AM

How does a client discover the new master after a Sentinel failover?

TofindthenewmasterafteraRedisSentinelfailover,clientsmustuseaSentinel-awarelibrary,provideSentineladdressesandthemastergroupname,detectconnectionbreakstore-querySentinels,optionallylistentopub/subeventslike switch-master,andcarefullymanageDNSorproxyl

Aug 05, 2025 am 11:07 AM

sentinel failover

How to check the remaining time to live for a key using TTL?

In Redis, use the TTL command to view the remaining survival time of the key. 1.TTLkey_name returns the remaining expiration time of the key. If the return integer greater than or equal to 0 indicates the remaining number of seconds; -1 indicates that the expiration time has not been set; -2 indicates that the key does not exist. 2. Modifying the key value will not reset the expiration time, and will only be updated if the expiration parameters such as EXPIRE are reset. 3. If millisecond precision is required, you can use the PTTL command. 4. TTL is often used for cache monitoring, current limiting mechanisms and debugging cache behaviors, such as for viewing the remaining time limit when the login fails to be limited. Mastering TTL and PTTL can effectively manage the Redis key life cycle.

Aug 05, 2025 am 04:58 AM

What is the SINTERCARD command introduced in Redis 7.0?

Redis7.0'sSINTERCARDcommandefficientlycomputestheintersectioncardinalityofmultiplesetswithoutreturningtheelements.Itavoidsmemoryinefficiencybynotgeneratingthefulllist,supportsoptionalLIMITtocapcomputation,andisidealforrecommendationsystemsorsocialnet

Aug 05, 2025 am 03:41 AM

What is Redis Pipelining and how does it improve performance?

RedisPipelining solves the problem of reducing round trip latency between clients and servers. Usually when multiple commands are sent, the client needs to wait for the response one by one, while Pipelining allows multiple commands to be sent at once and then read the response at once, significantly reducing the impact of network latency. When using it, you can queue up multiple commands and execute them once. For example, in Python, use redis.pipeline() to add set, get, delete commands and then call execute() to complete batch processing. Notes include: Not all commands can be piped, and do not reduce server processing time. Too many commands may increase memory consumption. Applicable scenarios include batch operation, high-delay connection, mutual

Aug 04, 2025 am 06:36 AM

Performance improvements

How to count the number of members within a score range using ZCOUNT?

The ZCOUNT command is used to count the number of members within the specified score range in the Redis ordered set. The basic usage is ZCOUNTkeyminmax. For example, ZCOUNTmyzset510 represents the number of members with a statistical score between 5 and 10; 1. By default, the range contains endpoints. If you want to exclude a certain endpoint, you can add (symbols, such as ZCOUNTleaderboard (8090 represents members with a statistical score greater than 80 and less than or equal to 90; 2. If ZCOUNT returns 0, possible reasons include that the key does not exist, all scores are not in the specified range, or the order of the minimum and maximum values is reversed; 3. When using it, you should pay attention to ensuring that min≤max, and confirm that the key exists and is an ordered set to avoid

Aug 04, 2025 am 01:15 AM

redis ZCOUNT

What is the difference between ZRANGE and ZREVRANGE?

ZRANGEretrieveselementsinascendingscoreorder,whileZREVRANGEreturnsthemindescendingorder.WhenworkingwithRedissortedsets,useZRANGEtogetthelowest-to-highestscores—idealforbottom-rankedentriesornaturalorderlistings—andZREVRANGEfortop-rankeditems,suchasst

Aug 04, 2025 am 01:05 AM

redis Sort collections

How to add one or more members to a Set using SADD?

TheSADDcommandinRedisaddsuniquememberstoaSet,automaticallyignoringduplicates.1.ItusesthesyntaxSADDkeymember[member...],creatingthekeyifitdoesn’texist.2.RedisensuresuniquenessbynotaddingduplicatevaluesalreadypresentintheSet.3.Multiplememberscanbeadded

Aug 04, 2025 am 12:13 AM

redis SADD

What are the atomicity guarantees of a Redis Lua script?

RedisLua scripts ensure data consistency through atomic execution. The core features and precautions are as follows: 1. The script is run in a single thread, and no other commands are inserted during execution to avoid race conditions; 2. If a script occurs when it is runtime error, the executed modifications will not be rolled back, and the application layer needs to handle exceptions; 3. Syntax errors prevent the script from running, and runtime errors lead to partial execution; 4. The script should be kept short and efficient to avoid blocking other requests.

Aug 03, 2025 am 03:51 AM

redis lua script

When should you use a Redis Hash instead of multiple top-level string keys?

Using RedisHash to store the critical value pairs is more appropriate because they save memory and support structured operations. 1. Hash is suitable for storing object-type data such as user information, with clear logic and easy maintenance; 2. Supports efficient acquisition of the entire object or atomic update of a single field; 3. Clear memory optimization, especially when there are few fields, compact encoding method is adopted; 4. Not suitable for scenarios where fields are not related, large fields need to be accessed separately, or single field expiration time needs to be set.

Aug 03, 2025 am 03:30 AM

字符串键

How to move an element from one list to another atomically using RPOPLPUSH?

RPOPLPUSH is a command in Redis to safely and atomically move elements from one list to another. 1. It pops up elements from the tail of the source list and pushes them to the head of the target list; 2. The entire operation is atomic to avoid data inconsistency caused by competition between multiple clients; 3. It is often used in scenarios such as task queues and message processing that need to ensure data consistency; 4. If the source list is empty or does not exist, return nil; 5. When the source and the target are in the same list, it realizes the loop rotation effect; 6. When actual use, check the return value and combine it with transaction or blocking variant optimization logic.

Aug 03, 2025 am 12:24 AM

atomicity