Shulou(Shulou.com)06/01 Report--

The usual use of MEMORY involves the following characteristics:

1. Operation-related transient, non-critical data management or cache, MEMORY table data is lost when MySQL processes crash or services restart.

2. Memory storage access is fast and latency is low. Data can be filled into memory without causing the operating system to swap into virtual memory.

Read only or read many data access modes.

MySQL Cluster provides similar functionality to MEMORY to improve performance, but provides additional features not supported by MEMORY, such as:

1. Row-level locking and multithreading, client reduces contention.

2. scalability of

3. Background operations for data persistence

4.shared-nothing structure, multi-host operation will not have a single point of error.

5. Automatic data distribution, the application does not need to participate in user sharding or partitioning solutions.

6. Variable length fields are supported, MEMORY does not.

If the columns of the MEMORY table hash index are contained in many indexes, the value of the date table field affects performance. The performance impact is related to being referenced by several indexes. You can avoid problems by using b-tree indexing.

The MEMORY table can be a non-unique key.

Index column value can be null

Physical properties of MEMORY table:

MEMORY storage engines have an associated disk file that holds table definitions. Table name.frm.

The MEMORY table has several properties:

MEMORY tables use small blocks, tables use dynamic hash storage, and there is no extra key space. Delete rows and put space into a linked list. It's reused when you insert it. MEMORY tables have no problem mixing insertions and deletions.

2. Memory table fixed length. Variable-length types such as varchar are also stored at fixed lengths.

3. Memory tables cannot contain BLOB,TEXT columns

4. MEMORY supports AUTO_INCREMENT column

5. No temporary memory table can be shared by all clients, but other temporary tables are the same.

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