Oracle UNDO表空间监控指南
<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li><a href="#_label0">一、基础监控方法</a></li><ul class="second_class_ul"><li><a href="#_lab2_0_0">1. 查看UNDO表空间基本信息</a></li><li><a href="#_lab2_0_1">2. 检查UNDO表空间使用率</a></li></ul><li><a href="#_label1">二、高级监控视图</a></li><ul class="second_class_ul"><li><a href="#_lab2_1_2">1. 使用V$UNDOSTAT视图</a></li><li><a href="#_lab2_1_3">2. 监控UNDO保留时间</a></li></ul><li><a href="#_label2">三、自动化监控策略</a></li><ul class="second_class_ul"></ul></ul></div><p class="maodian"><a name="_label0"></a></p><h2>一、基础监控方法</h2><p class="maodian"><a name="_lab2_0_0"></a></p><h3>1. 查看UNDO表空间基本信息</h3>
<div class="jb51code"><pre class="brush:sql;">SELECT ts.tablespace_name,
ts.status,
df.file_name,
df.bytes/1024/1024 AS "Size(MB)"
FROM dba_tablespaces ts
JOIN dba_data_files df ON ts.tablespace_name = df.tablespace_name
WHERE ts.contents = 'UNDO';
</pre></div>
<p>此查询显示UNDO表空间名称、状态、数据文件路径及大小‌</p>
<p class="maodian"><a name="_lab2_0_1"></a></p><h3>2. 检查UNDO表空间使用率</h3>
<div class="jb51code"><pre class="brush:sql;">SELECT a.tablespace_name,
ROUND(a.bytes/1024/1024/1024,0) "Total(GB)",
ROUND((a.bytes-b.bytes)/1024/1024/1024,0) "Used(GB)",
ROUND(b.bytes/1024/1024/1024,0) "Free(GB)",
ROUND(((a.bytes-b.bytes)/a.bytes)*100,2) "Used%"
FROM (SELECT tablespace_name, SUM(bytes) bytes
FROM dba_data_files GROUP BY tablespace_name) a,
(SELECT tablespace_name, SUM(bytes) bytes
FROM dba_free_space GROUP BY tablespace_name) b
WHERE a.tablespace_name = b.tablespace_name
AND a.tablespace_name IN ('UNDOTBS1','UNDOTBS2');
</pre></div>
<p>该查询计算UNDO表空间使用百分比‌</p>
<p class="maodian"><a name="_label1"></a></p><h2>二、高级监控视图</h2>
<p class="maodian"><a name="_lab2_1_2"></a></p><h3>1. 使用V$UNDOSTAT视图</h3>
<div class="jb51code"><pre class="brush:sql;">SELECT usn,
ROUND(rssize/1024/1024,2) "Undo Size(MB)",
wrcount "Write Count",
optcnt "Optimal Count",
expcnt "Expired Count",
unexpcnt "Unexpired Count"
FROM v$undostat;
</pre></div>
<p>此视图提供UNDO段统计信息，包括写入次数和过期块数量</p>
<p class="maodian"><a name="_lab2_1_3"></a></p><h3>2. 监控UNDO保留时间</h3>
<div class="jb51code"><pre class="brush:sql;">SELECT TO_CHAR(BEGIN_TIME, 'MM/DD/YYYY HH24:MI:SS') BEGIN_TIME,
TUNED_UNDORETENTION
FROM V$UNDOSTAT;
</pre></div>
<p>显示自动调整的UNDO保留时间</p>
<p class="maodian"><a name="_label2"></a></p><h2>三、自动化监控策略</h2>
<ol><li>设置告警阈值‌：建议当UNDO使用率超过80%时触发告警‌</li><li>定期健康检查‌：每日执行UNDO表空间使用情况检查，记录趋势变化</li><li>UNDO空间计算‌：通过公式估算所需空间：</li></ol>
<div class="jb51code"><pre class="brush:sql;">SELECT ur undo_retention,
dbs db_block_size,
ROUND((ur * (ups * dbs)) / 1024 / 1024,2) "Required(MB)"
FROM (SELECT value as ur FROM v$parameter WHERE name = 'undo_retention'),
(SELECT (sum(undoblks) / sum(((end_time - begin_time) * 86400))) ups FROM v$undostat),
(SELECT value as dbs FROM v$parameter WHERE name = 'db_block_size');
</pre></div>
<p>此公式基于UNDO保留时间和块大小计算所需空间‌</p>
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