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Home

Technical Articles

Database

Redis

How does optimistic locking work using WATCH, MULTI, EXEC?

Optimistic locking is a strategy used to handle concurrent modifications in a database or data store. Unlike pessimistic locks (blocking access before resource release), optimistic locks assume fewer conflicts, allowing clients to operate freely, but check whether other clients have modified the monitored key before applying the changes. In Redis, optimistic locking is implemented through WATCH, MULTI and EXEC commands: 1. The WATCH command monitors one or more keys. If these keys are modified before the transaction is executed, the transaction will fail; 2. The MULTI command enters transaction mode, and subsequent commands are queued and not executed immediately; 3. The EXEC command atomically executes all queued commands. If the monitored key is not changed, the execution will be successful, otherwise returning nil means the transaction failed. This mechanism

Aug 15, 2025 am 12:27 AM

watch optimistic locking

What is the difference between HSET, HMSET, and HSETNX?

HSET sets a single field and updates, HMSET sets multiple fields (old version), HSETNX sets only if the field does not exist. 1. HSET is used to add or update a single or multiple fields, returning the number of newly created or updated fields; 2. HMSET is used to set multiple fields in the old version of Redis, and is now replaced by multi-parameter HSET; 3. HSETNX ensures that the field exists for the first time to prevent overwriting existing values.

Aug 14, 2025 pm 07:13 PM

How to add a message to a Stream using XADD?

ToaddamessagetoaRedisstreamusingXADD,specifythekey,useforauto-generatedIDs,andprovidefield-valuepairs.1.Usetoauto-generatemessageIDs,ensuringuniquenessviatimestampandsequencenumber.2.SpecifycustomIDsintimestamp-sequenceformatwhenneeded,avoidingconfli

Aug 14, 2025 pm 02:52 PM

How to check if a value is a member of a Set using SISMEMBER?

Yes,youcancheckifavalueexistsinaRedisSetusingtheSISMEMBERcommand.1.TheSISMEMBERcommandchecksmembershipinasetwithsyntaxSISMEMBERkeymember,returning1ifthememberexists,0ifitdoesn’t,oranerrorifthekeyisnotaset.2.Commonusecasesincludecheckinguserlikes,veri

Aug 14, 2025 am 11:38 AM

How to troubleshoot a Redis instance that is consuming too much CPU?

HighCPUusageinRedisistypicallycausedbyinefficientqueries,excessiveclienttraffic,memorypressure,ormisconfigurations.Toaddressthis,first,checkforlargeorcomplexcommandslikeKEYS*,SMEMBERS,orLRANGEonbigdatasetsandreplacethemwithsaferalternativessuchasSCAN

Aug 14, 2025 am 11:18 AM

What's the Easiest Way to Install Redis on a Linux Server?

TheeasiestwaytoinstallRedisonaLinuxserverisbyusingthepackagemanager,specificallywiththesecommandsonUbuntu:1)sudoaptupdate,2)sudoaptinstallredis-server,whichensuresastableandcompatibleversionisinstalled.

Aug 13, 2025 am 10:48 AM

Can a replica accept writes?

Yes, some replicas can accept write operations, but it depends on the system architecture and configuration. 1. Most traditional databases default replicas are read-only to avoid data conflicts, but sets of postgreSQL logical replication and MongoDB replicas allow writing under specific conditions. 2. Multi-master replication architectures such as MariaDBMaxScale, GaleraCluster, etc. support multiple nodes to write simultaneously, but they need to deal with data conflicts and consistency issues. 3. Replica writing is generally not recommended, as it may lead to data inconsistency, synchronization delay and increase operation and maintenance complexity. Whether it should be written should be judged based on the specific system capabilities and needs.

Aug 13, 2025 am 06:05 AM

What Data Structures Does Redis Support That Traditional Databases Don't?

Redisstandsoutduetoitsuniquedatastructures:1)HyperLogLogforefficientcardinalityestimation,2)GeospatialIndexesforfastlocation-basedqueries,3)Streamsfortime-seriesdatamanagement,and4)Bitmapsfortrackingbinarystates,offeringflexibilityandperformancebeyon

Aug 13, 2025 am 04:52 AM

How to work with parts of a string using GETRANGE and SETRANGE?

GETRANGE is used to extract substrings of Redis strings, by specifying the start and end byte positions; SETRANGE is used to overwrite part of the string starting from the specified offset. For example, GETRANGEkey04 can get the first 5 characters, while SETRANGEkey6 "Redis" can replace the content starting from the 7th character. Note when using: ① The index starts at 0 and supports negative numbers; ② SETRANGE will be overwritten in place and will not insert or move characters; ③ The offset exceeds the current length will cause the string to expand and fill in empty bytes. Applicable scenarios include efficient partial updates, binary security operations and fixed format string processing, but the string structure must be ensured to be stable.

Aug 13, 2025 am 03:40 AM

String operations

What is a transaction in Redis and what are the MULTI/EXEC commands?

Redis transactions implement atomic operations through MULTI and EXEC commands, ensuring that multiple commands are executed in sequence and are not interfered by other clients. When using it, send MULTI to start the transaction first, then the sent command enters the queue without executing it immediately, and finally sends EXEC to execute all commands. If a command error occurs in a transaction, it will not roll back, and all commands will still be executed in turn. Suitable for scenarios where multiple keys need to be updated synchronously or ensure operational continuity, such as inventory deduction and sales count updates. Complex rollback logic is not supported, but more complex functions can be implemented through Lua scripts. Common precautions include: no pre-check, errors are exposed only during execution, and retry may be caused by WATCH conflicts under high concurrency.

Aug 12, 2025 am 05:18 AM

How to get the score of a specific member using ZSCORE?

Togetamember'sscoreinaRedissortedset,usetheZSCOREcommand.ItretrievesthescoreofaspecifiedmemberinO(1)time.1.Syntax:ZSCOREkeymember.2.Returnsthescoreasastring,ornilifthememberorkeydoesn'texist.3.Usecasesincludecheckinggamerankings,validatingmemberexist

Aug 12, 2025 am 04:35 AM

How Does Redis's In-Memory Approach Compare to Traditional Disk-Based Databases?

RedisisiDeal Foredandreal-Time Processing, WhiletraditionDital-Based Database Better Better Negotiation Larged Datasets DrobustDatapersistence.1) RedisExcelsinApplicationsRequingsub-Millisecondlatency, Likecachingandreal-Time Analytics, ButislimitedbymeMoryCo

Aug 12, 2025 am 01:20 AM

What are the pros and cons of AOF (Append-Only File) persistence?

AOF persistence ensures data security through record and write operations, but has low performance. Its advantage is that each write operation can reduce the risk of data loss, support the rewrite mechanism to compress the file volume, and have good file compatibility and can be edited manually; the disadvantage is that synchronous disk affects performance, files occupy more storage space, and slow recovery speed. The applicable scenario is an environment that emphasizes data integrity and accepts performance losses.

Aug 12, 2025 am 12:07 AM

What are the ACID properties of Redis transactions?

RedistransactionsdonotfullysupportACIDproperties.1.Atomicityispartial—commandsareexecutedasablock,buterrorsduringexecutiondonottriggerrollbacks.2.Consistencyismaintainedonlyifnoruntimeerrorsoccur,thoughRedislacksschemaenforcement.3.Isolationisstrongd

Aug 11, 2025 pm 11:23 PM