sql评估存储的速度和稳定性

该SQL计算最近30天内（AAS （Average Active Sessions）> 5的繁忙时段）该指标的平均值和方差，用于评估存储的速度和稳定性：

参看：https://mp.weixin.qq.com/s/9UEj1cDnMj4OAoAD1mQUpQ

SELECT ROUND(AVG(h.value), 4) AS average_latency,ROUND(VARIANCE(h.value), 4) AS variance_latency
FROM DBA_HIST_SYSMETRIC_HISTORY h
JOIN DBA_HIST_SNAPSHOT s ON h.snap_id = s.snap_id
JOIN DBA_HIST_SYSMETRIC_HISTORY b ON h.snap_id = b.snap_id
WHERE h.metric_name = 'Average Synchronous Single-Block Read Latency'AND s.begin_interval_time >= SYSDATE - 30AND b.metric_name = 'Average Active Sessions'AND b.value > 5AND h.value != 0;写法2：WITH high_activity_snapshots AS (SELECT DISTINCT s.snap_idFROM DBA_HIST_SNAPSHOT sJOIN DBA_HIST_SYSMETRIC_HISTORY b ON s.snap_id = b.snap_idWHERE s.begin_interval_time >= SYSDATE - 30AND b.metric_name = 'Average Active Sessions'AND b.value > 5
)
SELECT ROUND(AVG(h.value), 4) AS average_latency,ROUND(VARIANCE(h.value), 4) AS variance_latency
FROM DBA_HIST_SYSMETRIC_HISTORY h
JOIN high_activity_snapshots hs ON h.snap_id = hs.snap_id
WHERE h.metric_name = 'Average Synchronous Single-Block Read Latency'AND h.value !=0;

单位是毫秒（ms）。

• 平均值越低，表示读速度越快；

• 方差越小，表示性能越稳定。

结合两者，通过AWR快照数据了解存储在真实工作负载下的表现。