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Flash Cache works as follows:
The content stored in Flash Cache is controlled in two ways:
1. Flash Cache’s intelligent selection algorithm: determine by evaluating the frequency of access of data blocks and index blocks.
2. Modify the cell_flash_cache attribute of the database object.
Flash Cache storage content basic standards
Mainly small IO operations, as well as data blocks, index blocks, file headers, control files, etc. will be cached;
For RMAN backup IO operations, data pump IO operations, ASM mirroring operations, table space formatting, etc. will not be cached;
The cache priority of IO operations for full table scans is relatively low.
When data is stored in the flash Cache, it is mainly to improve the query speed. In other words, it is equivalent to adding a part of the buffer Cache area in addition to the memory, but the performance is better and the speed is better. Then, just like the buffer Cache, when the data in the flash Cache is full or written to a certain extent, the data needs to be written to the disk to leave space for new operation data.
Writing data in the cache to disk is called flushing. You can configure the Starting and stopping cache flushing levels value, which represents the percentage of the entire cache size occupied. When the data in the cache that has not been written to the disk reaches the starting flushing value, the controller starts flushing (written from the cache to the disk). When the amount of unwritten disk data in the cache is lower than the stop flush value, the flushing process stops.
If the start flushing level is set higher, more unwritten data can be cached in the memory. This helps improve the performance of write operations, but at the expense of data protection. If you want to get data protection, you can use lower start and stop values. Testing shows that the performance is better when using close start and stop flushing levels. If the stop level value is much lower than the start value, disk congestion will occur during flushing
Smart Flash LoggingFor a long time, the IO bottleneck of Redo log has been a major problem that has plagued the OLTP system, because the write delay of Redo directly drags down the response speed of the entire system and even the entire cluster.
In the traditional database architecture, some DBAs will separately allocate small block storage with low read and write latency to Redo. Starting from 11204, Oracle has proposed a new solution to specifically provide Redo in the flash memory area. Create an area to store temporary redo.
Place column storage in Flash Cache to improve write IO for frequently operated column storage objects
Application Container is a new component proposed in 12.2. It divides the database system under the same application into a sub-container to achieve relative business isolation and data security while ensuring the same management of multi-tenants.
PDB has its own undo table spaceStarting from 12.2, each PDB has its own undo tablespace. This eliminates contention between multiple PDBs. If you want to perform flashback or timestamp-based recovery, you only need to search in your own undo data to improve efficiency.
Flexible creation method of PDB1. Create from PDB$seed (or application root): by copying files
2. The existing PDB is created through hot clone
Note: In 12.1, when creating a new PDB based on a PDB, the original library needs to be opened in read only mode.
In 12.2, the original library can continue to perform DML operations without being affected.
After the cloning is completed, the data will continue to be refreshed to the new database.
3. Migration from PDBs in other CDBs: Relocate
The front-end executes a command such as create pluggable database from relocate, and the background will automatically execute remote hot clone and perform remote file copy and synchronization.
4. Generate a new PDB through shadow copy of ASM disk files.
PDB memory resource management
In a multi-tenant environment, multiple PDBs share memory resources. When a PDB needs to address buffer cache, it needs to search from the entire shared resources, which is very inconvenient. In 12.2, Oracle implemented PDB-based domain division for some resources.
The hash list of memory resources in 12.1 is as follows:
This is what happens in 12.2:
More new features of PDB
1. Character set: In 12.2, if the CDB character set is a superset, that is, AL32UTF8, then PDBs with different character sets are supported. At the same time, through Proxy PDB, PDBs with different character sets can be queried. Proxy will identify and make the character sets of both parties compatible without garbled characters.
Multi-tenant technology has been widely used by users, and Yunhe Enmo, as a leader in the data service industry, has helped users realize the cloud transformation of systems in the Internet era through the combination of zData solutions and Oracle multi-tenant.
For more detailed explanations of new features of multi-tenancy, please refer to
YH9:Oracle Multitenant Knowledge Base
Multi-tenant technology has been widely used by users. As a leader in the data service industry, Yunhe Enmo has helped users realize the cloud transformation of systems in the Internet era through the combination of zData solutions and Oracle multi-tenant.
Article from WeChat public account: Data and Cloud
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