Troubleshooting RDS Performance (MySQL, SQL SERVER and MongoDB)

I. Network Differences

1. Available Zones

ApsaraDB for RDS can be divided into single-zone and the multi-zone RDS. For single-zone RDS, the master and slave databases are in the same data centers, while for the multi-zone RDS, the master and slave databases are in different data centers. As a result, the ECS and RDS must be built in the same zone during RDS testing.

2. Network Links

ECS to RDS contains many network links, such as ECS — >DNS — >SLB — >Proxy — >DB. Self-built databases on ECS have 2 (ECS — >ECS), meaning RDS has 3 more links than self-built databases on ECS.

3. Case Study

  1. A particular online company found that performance had suffered after migrating its system to the cloud.
  2. The application code and database configuration are identical.

II. Configuration Differences

1. Specification Configuration

The RDS specification configuration mainly includes memory and CPU.
The ECS and RDS CPUs must have the same number of cores for RDS testing.

2. Parameter Configuration

(1) Security configuration: RDS applies the highest protection standards when committing transactions and flushing binlogs in order to better ensure data security.

  1. The sync_binlog parameter is the frequency at which the MySQL binlog syncs to disk. After the binlog is written sync_binlog times, it will be flushed to disk by MySQL. A value of 1 is the safest. It will synchronize the binary log once after writing each statement or transaction, so at most one statement or transaction log will be lost even in the event of total failure. The trade off is that this is the slowest configuration.

3. Case Study

  1. A user is migrating a local service system to the cloud
  2. The execution time on RDS is twice that of the offline self-built database

III. Framework differences

1. Master-Slave Mechanism

RDS utilizes a high availability operational model called the master-slave mechanism. At the same time, it also uses a semi-synchronous mechanism, which is an improvement on the asynchronous mechanism used by MySQL. After the master database finishes executing a transaction submitted by the client, it waits for acknowledgment from the slave database, which is responsible for writing the data to the relay log. Only then does the master database send the reply to the client, rather than sending it right away. The semi-synchronous mechanism offers data security improvements compared to the asynchronous mechanism, however it also causes a certain degree of latency, which is at least equal to the round-trip time for the TCP/IP connection. This means that the semi-synchronous mechanism increases the response time of the transaction.

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