1) Library Cache的命中率
公式:Library Cache Hit Ratio=SUM(PINHITS)/SUM(PINS)
SELECT SUM(PINHITS)/SUM(PINS) FROM V$LIBRARYCACHE;
命中率不能低于99%,否则需要考虑是否受共享池大小,绑定变量,cursor_sharing等因素的影响。
SELECT NAME,VALUE FROM V$PARAMETER WHERE NAME=‘cursor_sharing‘
2) Shared Pool的使用率
公式:Shared Pool Hit Ratio=(100-Free memory/shared_pool_size*100)%
如果数据库采用AMM方式管理内存使用以下语句获取Shared Pool大小:
SELECT POOL,ROUND(SUM(BYTES)/1024/1024,2) FROM V$SGASTAT where POOL=‘shared pool‘ group by POOL;
如果是采取Manual方式管理内存则:
SELECT NAME,VALUE FROM V$PARAMETER WHERE NAME=‘shared_pool_size‘;
查询1:
SELECT 100 - ROUND((SELECT ROUND(SUM(BYTES) / 1024 / 1024, 2) BYTES FROM V$SGASTAT WHERE NAME = ‘free memory‘ AND POOL = ‘shared pool‘ GROUP BY POOL) / ROUND(SUM(BYTES) / 1024 / 1024, 2), 4) * 100 || ‘%‘ RATIOS FROM V$SGASTAT where POOL = ‘shared pool‘ GROUP BY POOL
查询2:
SELECT 100 - ROUND(B.BYTES / ROUND(SUM(A.BYTES) / 1024 / 1024, 2),4)*100 || ‘%‘ RATIOS FROM V$SGASTAT A, (SELECT POOL,ROUND(SUM(BYTES) / 1024 / 1024, 2) BYTES FROM V$SGASTAT WHERE NAME = ‘free memory‘ AND POOL=‘shared pool‘ GROUP BY POOL) B where A.POOL = ‘shared pool‘ GROUP BY B.BYTES,A.POOL
共享池使用率应稳定在75%-90%间,过小则浪费,过大说明内存不足或语句重用性不高。
时间: 2024-10-02 16:20:53