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Technical Articles

Database

How to tune a SQL query in Oracle

IdentifytheproblematicqueryusingAWR,ASH,SQLTrace,orV$SQLtofindhigh-loadqueries;2.AnalyzetheexecutionplanviaEXPLAINPLANorDBMS_XPLANtodetectinefficiencieslikefulltablescansorjoinissues;3.Optimizequerystructurebyselectingonlyneededcolumns,usingEXISTSove

Aug 08, 2025 am 03:12 AM

How to Deal with Deadlocks in MySQL?

Deadlock cannot be completely avoided, but can be effectively managed through the following measures: 1. Catch deadlock errors in application code (such as MySQL's 1213 error) and retry the transaction. It is recommended to use exponential backoff delay; 2. Shorten the time when the transaction holds locks, move non-database operations out of the transaction and commit as soon as possible; 3. Access tables and rows in a consistent order in all transactions to prevent loop waiting; 4. Use a lower isolation level (such as READCOMMITTED) when allowed to reduce the use of gap locks; 5. Optimize indexes to reduce lock contention, ensure that query conditions, connections and sort fields use appropriate indexes; 6. Use SELECT...FORUPDATE and LOCKINSHAREMODE with caution, lock only necessary rows

Aug 08, 2025 am 03:07 AM

How does Oracle manage chained and migrated rows, and what is their performance impact?

Chained and migratedrows will affect Oracle performance due to additional I/O. Solutions include table restructuring, PCTFREE adjustment, etc. When the Chainedrows is inserted, the migratedrows is moved and the pointer is left after the update due to insufficient space. Both of them cause the query to be read multiple times; it can be detected through the ANALYZETABLE or CHAINED_ROWS view, and eliminated with ALTERTABLEMOVE or export import. At the same time, setting a higher PCTFREE, selecting the appropriate block size and partition can prevent problems; monitoring the "tablefetchcontinuedrow" statistical information can determine its impact, although there are few

Aug 08, 2025 am 02:47 AM

oracle performance

What Data Structures Does Redis Offer That Traditional Databases Lack?

Redisoffersuniquedatastructureslikestrings,lists,sets,sortedsets,hashes,HyperLogLogs,bitmaps,andgeospatialindexes,whichtraditionaldatabasestypicallydon'thave.1)Stringssupportatomicoperationsforcounters.2)Listsfunctionasefficientqueuesorstacks.3)Setsm

Aug 08, 2025 am 02:44 AM

傳統(tǒng)數(shù)據(jù)庫

How to create a foreign key relationship in Navicat?

The key steps to creating foreign keys in Navicat include: 1. Ensure that the two tables use the InnoDB engine; 2. Open the subtable design interface, switch to the "Foreign Keys" tab and add new records; 3. Select the foreign key field and the corresponding main table and primary key field; 4. Set the behavior during update and deletion (such as RESTRICT, CASCADE, SETNULL); 5. Ensure that the field types are consistent and the foreign key fields have indexes. If the field definition conflicts, you need to adjust first. The entire process is done through a graphical interface without writing SQL.

Aug 08, 2025 am 02:39 AM

Mastering CRUD Operations in MongoDB for Modern Applications

MasteringCrudinMongodbrequiresDelingitsdocument Basedbson Modelforflexibledatamement.2.Ussertone () BervesinsertsandinsertMine () ForeffiTrientBulk operations, Whilevalidating data dandindexingfieldshandshandshand.

Aug 08, 2025 am 02:22 AM

mongodb crud

How to perform a failover in Oracle Data Guard

Confirmtheprimaryisdownandswitchoverisnotpossiblebeforeinitiatingfailover.2.EnsureallredologsareappliedonthestandbybycheckingV$ARCHIVED_LOGandregisteringanymissinglogsifnecessary.3.CancelmanagedrecoverywithALTERDATABASERECOVERMANAGEDSTANDBYDATABASEFI

Aug 08, 2025 am 01:21 AM

How to find orphaned records in a database in SQL?

Orphanedrecordsoccurwhenachildrecordreferencesanon-existentparentrecord,typicallyduetomissingreferentialintegrity.2.Tofindthem,useaLEFTJOINbetweenthechildandparenttablesandfilterwheretheparentkeyisNULL,suchas:SELECTo.FROMordersoLEFTJOINusersuONo.user

Aug 08, 2025 am 12:51 AM

What is Redis and how does it differ from traditional databases?

Redisisanin-memorydatastoreusedasadatabase,cache,andmessagebroker,excellinginspeedandversatility.Itstoresdatainmemoryforfastperformance,supportsvariousdatastructures,andusesasimplecommandinterface,butlacksthedurabilityandcomplexquerycapabilitiesoftra

Aug 08, 2025 am 12:44 AM

What is a temporary table in SQL?

TemporarytablesinSQLaresession-specific,automaticallydroppedwhennolongerneeded,andusedforintermediatestoragetosimplifycomplexqueries.1.Theyimproveperformancebybreakingdowncomplexqueriesintosteps.2.Theystoreintermediateresultsforreuse.3.Theysimplifyqu

Aug 08, 2025 am 12:31 AM

How to set read-only mode for a connection?

The methods for setting database connections to read-only mode include: 1. Setting through connection string parameters; 2. Setting at the session level; 3. Implementing at the application level. For PostgreSQL, MySQL, and SQLServer, read-only parameters can be specified in the connection string, such as SQLServer uses ApplicationIntent=ReadOnly. If it cannot be set through the connection string, you can enable read-only mode in the current session by executing commands. For example, PostgreSQL uses SETLOCALdefault_transaction_read_only=on, and MySQL uses SETSESSIONread_on.

Aug 08, 2025 am 12:27 AM

How to check a table for errors in MySQL

UsetheCHECKTABLEcommandtodirectlycheckforerrors:CHECKTABLEtable_name;aresultof"OK"intheMsg_textcolumnindicatesnoissues,whilevalueslike"Corrupt"signalproblems.2.Understandcommonerrortypessuchasindexorrowdatacorruption,incorrectauto

Aug 07, 2025 pm 11:57 PM

How to handle transactions with SAVEPOINT in MySQL

SAVEPOINTinMySQLallowspartialrollbackwithinatransaction,preservingearlierwork;2.StartwithSTARTTRANSACTIONorBEGIN;3.SetasavepointusingSAVEPOINTsavepoint_name;4.RollbacktoitwithROLLBACKTOSAVEPOINTifanerroroccurs;5.Continuethetransactionorcommitafterrol

Aug 07, 2025 pm 11:56 PM

mysql

Optimizing MySQL for Search Engines and SEO Applications

To optimize MySQL for search engines and SEO tools, the first thing to do is to use the InnoDB storage engine is to create indexes reasonably, the third thing to adjust the configuration to accommodate loads with more reads and less writes, and the fourth thing to partition large tables if necessary. Specifically, InnoDB supports transaction and row-level locks, which are suitable for frequent updates and batch insertions; indexes should be created for common query conditions such as WHERE and ORDERBY, while avoiding excessive indexing; in terms of configuration, it focuses on optimizing parameters such as innodb_buffer_pool_size, innodb_io_capacity, etc.; for data tables with more than millions of rows, query efficiency can be improved and old data cleaning can be simplified by partitioning by date range.

Aug 07, 2025 pm 11:54 PM

mysql seo