LOB_DATA doesn't get deallocated

  • Hi...

    I seem to have a problem getting some LOB_DATA deallocated.

    The problem only occurs if the read_committed_snapshot is set to ON. If i issue a truncate table the data is deallocated correctly

    Alter database to read_committed_snapshot ON

    USE master

    alter database VARBIN_Test set read_committed_snapshot ON

    Create a table

    USE [VARBIN_Test]

    GO

    /****** Object: Table [dbo].[AAAEDRW_CALL_ASSEMBLY] Script Date: 12/15/2010 09:58:33 ******/

    SET ANSI_NULLS ON

    GO

    SET QUOTED_IDENTIFIER ON

    GO

    SET ANSI_PADDING ON

    GO

    CREATE TABLE [dbo].[AAAEDRW_CALL_ASSEMBLY](

    [CA_PART_ID] [numeric](18, 0) IDENTITY(1,1) NOT NULL,

    [CA_ASSEMBLE_KEY] [varchar](255) NOT NULL,

    [CA_RECORD_SEQUENCE] [numeric](18, 0) NULL,

    [CA_TRANSACTION_ID] [numeric](18, 0) NULL,

    [CA_LAST_MODIFIED] [numeric](18, 0) NULL,

    [CA_RECORD_STATE] [numeric](18, 0) NULL,

    [CA_SERIALIZED_RECORD] [varbinary](max) NULL,

    [CA_BOT_NAME] [varchar](255) NOT NULL,

    [CA_SORTING_ID] [numeric](18, 0) NULL,

    CONSTRAINT [AAAPK_EDRW_CALL_ASSEMBLY] PRIMARY KEY CLUSTERED

    (

    [CA_BOT_NAME] ASC,

    [CA_PART_ID] ASC

    )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]

    ) ON [PRIMARY]

    GO

    SET ANSI_PADDING OFF

    GO

    Insert records (att. large record text)

    USE VARBIN_Test

    declare @Cnt integer = 1

    while @Cnt < 10000

    begin

    Set @Cnt = @Cnt+1

    INSERT INTO [AAAEDRW_CALL_ASSEMBLY]

    ([CA_ASSEMBLE_KEY]

    ,[CA_RECORD_SEQUENCE]

    ,[CA_TRANSACTION_ID]

    ,[CA_LAST_MODIFIED]

    ,[CA_RECORD_STATE]

    ,[CA_SERIALIZED_RECORD]

    ,[CA_BOT_NAME]

    ,[CA_SORTING_ID])

    values (3537323734323239+@Cnt, 1, 2163856063332879+@Cnt, 1274786288+@Cnt,0,

    convert (varbinary(max),@Cnt) +

    convert (varbinary(max),

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    '123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890'),

    'ESGSN Call Assembly', 1274786288+@Cnt)

    END

    Delete some records

    begin transaction

    Delete from [AAAEDRW_CALL_ASSEMBLY] where ((CA_PART_ID % 5) = 0)

    commit

    go

    begin transaction

    Delete from [AAAEDRW_CALL_ASSEMBLY] where ((CA_PART_ID % 4) = 0)

    commit

    begin transaction

    Delete from [AAAEDRW_CALL_ASSEMBLY] where ((CA_PART_ID % 3) = 0)

    commit

    go

    begin transaction

    Delete from [AAAEDRW_CALL_ASSEMBLY] where ((CA_PART_ID % 2) = 0)

    commit

    delete from [AAAEDRW_CALL_ASSEMBLY] where CA_PART_ID not In (Select top 945 CA_PART_ID from [AAAEDRW_CALL_ASSEMBLY])

    Check usage

    DECLARE @db_id SMALLINT;

    DECLARE @object_id INT;

    SET @db_id = DB_ID(N'VARBIN_Test');

    SET @object_id = OBJECT_ID(N'[dbo].[AAAEDRW_CALL_ASSEMBLY]');

    SELECT alloc_unit_type_desc,

    page_count,

    avg_page_space_used_in_percent,

    record_count

    FROM sys.dm_db_index_physical_stats(@db_id, @object_id, NULL, NULL , 'Detailed');

    Neither rebuild or reorganize index with LOB_COMPACTION helps here. dbcc cleantable doenst do anything either.

    If i repeat the process with

    USE master

    alter database VARBIN_Test set read_committed_snapshot OFF

    everything looks as i expect

    What have i missed?

    Best regards

    /Jesper

  • Described behavior appears to be closely related to bug #50002862

    Do you really need snapshot isolation or was it just a test?

    _____________________________________
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at Amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
  • According to our supplier the application needs the snapshot isolation in order to avoid some locking issues.

    Where can i find information on the bug you mention, are there any workarounds?

    Best regards

    /Jesper

  • jln (12/15/2010)


    According to our supplier the application needs the snapshot isolation in order to avoid some locking issues.

    Where can i find information on the bug you mention, are there any workarounds?

    Microsoft's Knowledge Base is the primary source of information for these kind of things, start here... http://support.microsoft.com/kb/953991

    _____________________________________
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at Amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
  • Thanks, I just tried to Google it.

    I should have tried harder.

    I think I actually saw this some time back but disconsidered it as it was reported fixed.

    We are running a:

    Microsoft SQL Server 2008 (SP2) - 10.0.4000.0 (X64) Sep 16 2010 19:43:16 Copyright (c) 1988-2008 Microsoft Corporation Enterprise Edition (64-bit) on Windows NT 6.0 <X64> (Build 6002: Service Pack 2)

    I delayed testing it anew until we recently applied SP2 to this environment.

    So I basically need to go talk to SQL server support at Microsoft on this issue

    Best regards

    /Jesper

  • jln (12/15/2010)


    I think I actually saw this some time back but disconsidered it as it was reported fixed.

    So I basically need to go talk to SQL server support at Microsoft on this issue

    It wouldn't be the first time a bug comes back to life or is "re-introduced" as official documentation uses to say.

    Opening a ticket with Microsoft Support wouldn't hurt at all - you have a test case.

    My guess it that this behavior is either caused by a "bug" or a "feature" - only Microsoft can tell the difference 🙂

    _____________________________________
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at Amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
  • I will open a ticket.

    I just didn't want to do that if I hadn't understood correctly what i saw 🙂

    Thanks for your time to look into this.

    I will update the thread when i get a reply from MS

    Best regards

    /Jesper

  • We ended up closing the ticket with Microsoft

    After some time the problem disappeared on our production system.

    We were still able to reproduce on our test environment, but elected to close the issue as we didn't want to use the resources on a problem that no longer existed in production.

    Thanks for your patience

    /Jesper

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