0

以下查询导致 SQL Server 2014 TEMPDB.MDF 增长到 40Gb，运行大约需要一个小时。

NVARCHAR(MAX)对不需要几分钟的列的类似查询。

正在更新的表大约有 700 万行。

添加AND C.SQLStmt IS NOT NULL到最后改善了这一点。

任何帮助，将不胜感激。

UPDATE R 
SET    R.SQLStmt = C.SQLStmt 
FROM SampleResults R 
  JOIN SampleTests T ON T.SampleCode = R.SampleCode 
                    AND T.TestPosition = R.TestPosition 
  JOIN TestComponents C ON T.TestCode = C.TestCode 
                       AND T.TestVersion = C.AuditNumber 
                       AND R.ComponentColumn = C.ComponentColumn 
                       AND R.ComponentRow = C.ComponentRow 
WHERE T.AuditFlag = 0 
AND   R.AuditFlag = 0 
AND   C.SQLStmt IS NOT NULL

这是从这个问题开始的，我没有足够的声誉来评论。

执行计划是：

Update
Cost: 0%
 |
Cluseterd Index Updated
[SampleResults].[pk_SampleResults]
Cost: 27%
 |
Top
COST: 0%
 |
Sort
(Distinct Sort)
Cost: 31%
 |
Nested Loops   Index Seek (NonClustered)
(Inner Join) - [SampleTests].[SampleTestsAuditFlag...
Cost: 0%       Cost: 10%
 |
Nested Loops   Key Lookup (Clustered)
(Inner Join) - [SampleResults].[pk_SampleResults]...
Cost: 0%       Cost: 15%
 |
Nested Loops   Index Seek (NonClustered)
(Inner Join) - [SampleResults].[SampleResultsCompo...
Cost: 0%       Cost: 9%
 |
Filter
Cost: 0%
 |
Clustered Index Scan (Clustered)
[TestComponents].[pk_TestComponents...
Cost: 9%
4

1 回答 1

0

由于该列实际存储的数据最大大小仅为 392 个字符，因此最终的解决方案是：

1) 暂时将源列和目标列（SampleResults.SQLStmt 和 TestComponents.SQLStmt）的大小更改为 392 个字符。2) 进行更新。3) 将源列和目标列的大小更改为新的更合理的 4000 个字符大小。

DECLARE @tempSQLStmtLength SMALLINT = (SELECT MAX(LEN(SQlStmt)) FROM TestComponents WHERE SQlStmt IS NOT NULL)
IF @tempSQLStmtLength IS NOT NULL AND @tempSQLStmtLength > 0
BEGIN
  -- Temporarily reduce size of SQLStmt columns so that update is as quick as possible.
  EXEC('ALTER TABLE SampleResults ALTER COLUMN SQLStmt NVARCHAR(' + @tempSQLStmtLength +') NULL')
  EXEC('ALTER TABLE TestComponents ALTER COLUMN SQLStmt NVARCHAR(' + @tempSQLStmtLength + ') NULL')

  -- Perform update.
  UPDATE R SET R.SQLStmt = C.SQLStmt FROM SampleResults R JOIN SampleTests T ON T.SampleCode = R.SampleCode AND T.TestPosition = R.TestPosition JOIN TestComponents C ON (T.TestCode = C.TestCode OR T.TestCode + '-' + CAST(T.TestPosition AS VARCHAR(5)) + '-' + T.SampleCode = C.TestCode) AND T.TestVersion = C.AuditNumber AND R.ComponentColumn = C.ComponentColumn AND R.ComponentRow = C.ComponentRow WHERE T.AuditFlag = 0 AND R.AuditFlag = 0 AND C.SQLStmt IS NOT NULL

  -- Now that update is finished, set SQLStmt columns to their final new size.
  ALTER TABLE SampleResults ALTER COLUMN SQLStmt NVARCHAR(4000) NULL
  ALTER TABLE TestComponents ALTER COLUMN SQLStmt NVARCHAR(4000) NULL
END;

TEMPDB.MDB 只增长到 2.8Gb 并且需要几分钟。

于 2018-03-27T11:10:12.740 回答