Oracle AUTOTRACE statistics

Oracle AUTOTRACE statistical information explanation of statistical information in AUTOTRACE: www.2cto.com recursive cals: RECURSIVE read to ensure the smooth execution of user-sent SQL statements, ORACLE must execute some additional statements. These statements are called recursive reads. For example, if you want to insert data entries but do not have enough table space, ORALCE will generate recursive reads to dynamically allocate space. When the data dictionary information does not exist in the data dictionary cache and needs to be read from the hard disk, it also needs to be read recursively. It generates a maintenance statement internally, and there will be a recursive read. Db block gets: The data BLOCK read from the buffer cache in real-time read mode. At any time, there is only one current data BLOCK in the buffer cache. Real-time reading usually occurs when you modify or delete data. Www.2cto.com consistent gets: Number of logical reads generated by CONSISTENT reads. Data blocks read from the buffer cache in consistent read mode. If the data changes, the data is read from the undo segment to ensure consistency of data reading. What is consistent read: ORACLE is a multi-user system. Before a session starts to read data, it may modify the data to be read by another session. If the session reads the modified data, data inconsistency may occur. Consistent reading is to ensure data consistency. The data block in the buffer cache has the SCN of the last data block modification. If a transaction needs to modify the data in the data block, it will first save a copy of the data block before the modification and the data block of the SCN In the rollback segment, then, update the data block and Its SCN in the buffer cache, and identify it as "dirty" data. When other processes read data blocks, the SCN on the data blocks and their own SCN are compared first. If the SCN on the data block is smaller than or equal to the SCN of the process itself, the data on the data block is directly read; if the SCN on the data block is greater than the SCN of the process itself, the data block read before the modification is located in the rollback segment. Generally, common queries are consistent reads. Www.2cto.com physical reads: Number of physical reads. When a data block is read for the first time, it is cached in the buffer cache, and the second time the data block is read and modified, it is stored in the buffer cache in the memory. When new data needs to be read into the buffer cache, And the buffer cache does not have enough free space, Oracle will replace the LRU data in the LRU linked list based on the LRU algorithm. When the data is accessed again, it needs to be read from the disk into the buffer cache again. SIZE of logs generated by redo size bytes sent via SQL * net to client server bytes sent to client via SQL * net bytes ed via SQL * net from client sent to SQL * NET number of bytes: www.2cto.com SQL * NET ROUNDTRIPS TO/FROM the number of times the CLIENT Server communicates with the CLIENT SORTS (MEMORY) memory sort operations SORTS (DISK) DISK sort operations rows processed operations generate data volume logical READ = db block gets + consistent gets; physical read = physical reads; buffer cache hit rate = logical read/(physical read + logical read );