Redis transaction and watch instruction

1. Redis Affairs and watch Instructions
   1. Redis Business
   2. watch Instructions
   3. summary
   4. ️ Thank you for your

Redis Affairs and watch Instructions

Redis Business

redis Our business is MULTI Instructions indicate that things are open , Sent by the client after the service is opened EXEC DISCARD WATCH MULTI The order is executed immediately , Other instructions will be put into the business queue , Then come back and send a message to the client ：QUEUE

When the client sends... To the server EXEC Time of instruction , The server traverses the business queue of the client , Carry out all instructions saved , And return all the performance results to the client .

watch Instructions

watch The directive is able to monitor multiple database keys , When excc The time when the order is fulfilled , If the monitored database key has been modified , Failure in business performance , The principle is redis There are in the database watched_keys Dictionaries , Dictionary keys are watch Command supervised database key , Values are linked lists , Record all client information that monitors this key .

When the database modification instruction is executed, it will call touchWatchedKey function ,touchWatchedKey Function will set the client of the correction key CLIENT_DIRTY_CAS identification

//  When key Corrected , Call this function void signalModifiedKey(redisDb *db, robj *key) {    touchWatchedKey(db,key);}// Touch  One  key, If we should key Being supervised , Then the client will perform EXEC defeat void touchWatchedKey(redisDb *db, robj *key) {    list *clients;    listIter li;    listNode *ln;    //  If there is no supervised in the database key, Come straight back     if (dictSize(db->watched_keys) == 0) return;    //  Find out what to supervise key Of client Linked list     clients = dictFetchValue(db->watched_keys, key);    //  Not found back     if (!clients) return;    /* Mark all the clients watching this key as CLIENT_DIRTY_CAS */    /* Check if we are already watching for this key */    listRewind(clients,&li);    //  Traverse everything to supervise the key Of client    while((ln = listNext(&li))) {        client *c = listNodeValue(ln);        //  Set up CLIENT_DIRTY_CAS identification         c->flags |= CLIENT_DIRTY_CAS;    }}

Then the server receives a message from the client exec When the command , The server depends on the client CLIENT_DIRTY_CAS Identification judgment , If there is this sign , The description has been corrected , The server will reject the business submitted by the client .

summary

This is it. redis Relevant contents of the transaction , The transaction is started through MULTI command , All commands go into the transaction queue , When executed exec When ordered , The commands in the transaction queue are submitted together ,watch Command to monitor keys , When a key is modified during a transaction , The monitor corresponding to this key can detect , Then the transaction will fail to commit , Ensure transaction consistency .

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