Prdp Prdp - 20 days ago 4
SQL Question

Table Valued Constructor Maximum rows limit in Select

I have a

Table Valued Constructor
through which am Selecting around
1 million
records. It will be used to
update
another table.

SELECT *
FROM (VALUES (100,200,300),
(100,200,300),
(100,200,300),
(100,200,300),
.....
..... --1 million records
(100,200,300)) tc (proj_d, period_sid, val)


Here is my original query : https://www.dropbox.com/s/ezomt80hsh36gws/TVC.txt?dl=0#

When I do the above
select
it is simply showing Query completed with errors with showing any error message.

enter image description here

Update : Tried to catch the error message or error number using
TRY/CATCH
block but no use still same error as previous image

BEGIN try
SELECT *
FROM (VALUES (100,200,300),
(100,200,300),
(100,200,300),
(100,200,300),
.....
..... --1 million records
(100,200,300)) tc (proj_d, period_sid, val)
END try

BEGIN catch
SELECT Error_number(),
Error_message()
END catch


Why it is not executing is there any limit for Table Valed constructor in
Select
. I know for
Insert
it is
1000
but am selecting here.

Answer

There's no relevant hard coded limit (65,536 * Network Packet Size of 4KB is 268 MB and your script length is nowhere near that) though it is inadvisable to use this method for a large amount of rows.

The error you are seeing is thrown by the client tools not SQL Server. If you construct the SQL String in dynamic SQL compilation is able to at least start successfully

DECLARE @SQL NVARCHAR(MAX) = '(100,200,300),
';

SELECT @SQL = 'SELECT * FROM (VALUES ' + REPLICATE(@SQL, 1000000) + '
(100,200,300)) tc (proj_d, period_sid, val)';

SELECT @SQL AS [processing-instruction(x)]
FOR XML PATH('')

SELECT DATALENGTH(@SQL) / 1048576.0 AS [Length in MB] --30.517705917

EXEC(@SQL);

Though I killed the above after ~30 minutes compilation time and it still hadn't produced a row. The literal values need to be stored inside the plan itself as a table of constants and SQL Server spends a lot of time trying to derive properties about them too.

SSMS is a 32 bit application and throws a std::bad_alloc exception whilst parsing the batch

enter image description here

It tries to push an element onto a vector of Token that has reached capacity and its attempt to resize fails due to unavailability of a large enough contiguous area of memory. So the statement never even makes it as far as the server.

The vector capacity grows by 50% each time (i.e. following the sequence here). The capacity that the vector needs to grow to depends on how the code is laid out.

The following needs to grow from a capacity of 19 to 28.

SELECT * FROM 
(VALUES 
(100,200,300),
(100,200,300),
(100,200,300),
(100,200,300),
(100,200,300),
(100,200,300)) tc (proj_d, period_sid, val)

and the following only needs a size of 2

SELECT * FROM (VALUES (100,200,300),(100,200,300),(100,200,300),(100,200,300),(100,200,300),(100,200,300)) tc (proj_d, period_sid, val)

The following needs a capacity of > 63 and <= 94.

SELECT *
FROM   (VALUES 
      (100,
       200,
       300),
      (100,
       200,
       300),
      (100,
       200,
       300),
      (100,
       200,
       300),
      (100,
       200,
       300),
      (100,
       200,
       300)
       ) tc (proj_d, period_sid, val) 

For a million rows laid out as in case 1 the vector capacity needs to grow to 3,543,306.

You might find that either of the following will allow the client side parsing to succeed.

  1. Reduce the number of line breaks.
  2. Restarting SSMS in the hope that the request for large contiguous memory succeeds when there is less address space fragmentation.

However even if you do successfully send it to the server it will only end up killing the server during execution plan generation anyway as discussed above.

You'll be much better off using the import export wizard to load the table. If you must do it in TSQL you'll find breaking it into smaller batches and/or using another method such as shreding XML will perform better than Table Valued Constructors. The following executes in 13 seconds on my machine for example (though if using SSMS you'd still likely have to break up into multiple batches rather than pasting a massive XML string literal).

DECLARE @S NVARCHAR(MAX) = '<x proj_d="100" period_sid="200" val="300" />
' ; 

DECLARE @Xml XML = REPLICATE(@S,1000000);

SELECT 
    x.value('@proj_d','int'),
    x.value('@period_sid','int'),
    x.value('@val','int')
FROM @Xml.nodes('/x') c(x)
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