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ASE15.7 optimzer :"log scan"

0 Kudos

Hi

we are runing a in-house apps and having performance issues/blockig when runing a showplan I see  same table with "Log Scan" what does this means ? , this table  has > 10 mil rows

1

        The type of query is UPDATE.

    5 operator(s) under root

       |ROOT:EMIT Operator (VA = 5)

       |

       |   |UPDATE Operator (VA = 4)

       |   |  The update mode is deferred.

       |   |

       |   |   |NESTED LOOP JOIN Operator (VA = 3) (Join Type: Inner Join)

       |   |   |

       |   |   |   |RESTRICT Operator (VA = 1)(0)(0)(0)(4)(0)

       |   |   |   |

       |   |   |   |   |SCAN Operator (VA = 0)

       |   |   |   |   |  FROM TABLE

       |   |   |   |   |  mfs_files

       |   |   |   |   |  d

       |   |   |   |   |  Log Scan.

       |   |   |   |   |  Forward Scan.

       |   |   |   |   |  Positioning at start of table.

       |   |   |   |   |  Using I/O Size 2 Kbytes for data pages.

       |   |   |   |   |  With MRU Buffer Replacement Strategy for data pages.

       |   |   |

       |   |   |   |SCAN Operator (VA = 2)

       |   |   |   |  FROM TABLE

       |   |   |   |  adMirrorUsage

       |   |   |   |  m

       |   |   |   |  Using Clustered Index.

       |   |   |   |  Index : mirrorID

       |   |   |   |  Forward Scan.

       |   |   |   |  Positioning by key.

       |   |   |   |  Keys are:

       |   |   |   |    mirrorID ASC

       |   |   |   |  Using I/O Size 2 Kbytes for index leaf pages.

       |   |   |   |  With LRU Buffer Replacement Strategy for index leaf pages.

       |   |   |   |  Using I/O Size 2 Kbytes for data pages.

       |   |   |   |  With LRU Buffer Replacement Strategy for data pages.

       |   |

       |   |  TO TABLE

       |   |  adMirrorUsage

       |   |  Using I/O Size 2 Kbytes for data pages.

Total estimated I/O cost for statement 10 (at line 30): 136.

QUERY PLAN FOR STATEMENT 11 (at line 37).

Optimized using Serial Mode

    STEP 1

        The type of query is UPDATE.

    4 operator(s) under root

       |ROOT:EMIT Operator (VA = 4)

       |

       |   |UPDATE Operator (VA = 3)

       |   |  The update mode is deferred.

       |   |

       |   |   |NESTED LOOP JOIN Operator (VA = 2) (Join Type: Inner Join)

       |   |   |

       |   |   |   |SCAN Operator (VA = 0)

       |   |   |   |  FROM TABLE

       |   |   |   |  mfs_files

       |   |   |   |  d

       |   |   |   |  Log Scan.

       |   |   |   |  Forward Scan.

       |   |   |   |  Positioning at start of table.

       |   |   |   |  Using I/O Size 2 Kbytes for data pages.

       |   |   |   |  With MRU Buffer Replacement Strategy for data pages.

       |   |   |

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