ExecuteReader Blocks Inserts on a Table

[Charles Law]

I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through the
rows, writing them out to a file. This takes about 5 minutes until I close
the reader.

Whilst this is going on, I have another application that is trying to insert
rows into the table. Normally, the inserts happen straight away, but when
the reader is open each insert takes a very long time to complete.

I realise that this is not an unreasonable thing to happen, given that I am
trying to write to the table whilst reading from it, but the rows being
written will never be included in the WHERE clause in my select statement,
and even if they were (which they won't), I wouldn't want them included in
the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[=?Utf-8?B?S2VycnkgTW9vcm1hbg==?=]

Charles,

Are the 2 applications on the same machine or different machines?

Is the database server on a different machine than the applications?

Kerry Moorman
"Charles Law" wrote:

I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through the
rows, writing them out to a file. This takes about 5 minutes until I close
the reader.

Whilst this is going on, I have another application that is trying to insert
rows into the table. Normally, the inserts happen straight away, but when
the reader is open each insert takes a very long time to complete.

I realise that this is not an unreasonable thing to happen, given that I am
trying to write to the table whilst reading from it, but the rows being
written will never be included in the WHERE clause in my select statement,
and even if they were (which they won't), I wouldn't want them included in
the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[Cor Ligthert[MVP]]

Charles,

You are by the way not using transaction locking, because then this is the
normal behaviour.

Cor

"Charles Law" <bl***@nowhere. comschreef in bericht
news:Om******** ******@TK2MSFTN GP06.phx.gbl...

>I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through
the rows, writing them out to a file. This takes about 5 minutes until I
close the reader.

Whilst this is going on, I have another application that is trying to
insert rows into the table. Normally, the inserts happen straight away,
but when the reader is open each insert takes a very long time to
complete.

I realise that this is not an unreasonable thing to happen, given that I
am trying to write to the table whilst reading from it, but the rows being
written will never be included in the WHERE clause in my select statement,
and even if they were (which they won't), I wouldn't want them included in
the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[Jack Jackson]

On Thu, 19 Jun 2008 02:17:57 +0100, "Charles Law" <bl***@nowhere. com>
wrote:

>I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through the
rows, writing them out to a file. This takes about 5 minutes until I close
the reader.

Whilst this is going on, I have another application that is trying to insert
rows into the table. Normally, the inserts happen straight away, but when
the reader is open each insert takes a very long time to complete.

I realise that this is not an unreasonable thing to happen, given that I am
trying to write to the table whilst reading from it, but the rows being
written will never be included in the WHERE clause in my select statement,
and even if they were (which they won't), I wouldn't want them included in
the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

You might take a look at the Transact-SQL statement SET TRANSACTION
ISOLATION LEVEL.

[Tibor Karaszi]

If the SELECT limits itself using a WHERE clause to rows which aren't in the inserted set, then you
have a chance to have the SELECT not blocked by your INSERTs. But that also depends on what
execution plan you get. If SQL Server drive the SELECT using an index which is on something that can
be used to exclude the rows to INSERT then you shouldn't see this blocking. However, considering you
return so many rows, you need to carefully evaluate your indexing strategy as well as your SELECT
query to make this happen.

Other options include Snapshot isolation and the READPAST optimizer hint. Those are well documented
in Books Online.

--
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://sqlblog.com/blogs/tibor_karaszi
"Charles Law" <bl***@nowhere. comwrote in message news:Om******** ******@TK2MSFTN GP06.phx.gbl...

>I have a sproc that returns data from a table using a simple SELECT. There are quite a few rows
returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through the rows, writing them
out to a file. This takes about 5 minutes until I close the reader.

Whilst this is going on, I have another application that is trying to insert rows into the table.
Normally, the inserts happen straight away, but when the reader is open each insert takes a very
long time to complete.

I realise that this is not an unreasonable thing to happen, given that I am trying to write to the
table whilst reading from it, but the rows being written will never be included in the WHERE
clause in my select statement, and even if they were (which they won't), I wouldn't want them
included in the selected rows.

Is there a way to read rows so that inserts can still occur without blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[Charles Law]

Hi Kerry

The two applications are on different machines, connected by a fairly slow
link, which is why it takes so long to iterate through the rows returned by
the reader. The database server is clustered on another machine, which is on
a Gb link to the second application, but the first (reader) application is
at the other end of the slow connection.

I could run both on the same machine, but then I would have to transfer the
resulting file over the slow link, and that would take longer in real time.

Charles
"Kerry Moorman" <Ke**********@d iscussions.micr osoft.comwrote in message
news:6A******** *************** ***********@mic rosoft.com...

Charles,

Are the 2 applications on the same machine or different machines?

Is the database server on a different machine than the applications?

Kerry Moorman
"Charles Law" wrote:

>I have a sproc that returns data from a table using a simple SELECT.
There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through
the
rows, writing them out to a file. This takes about 5 minutes until I
close
the reader.

Whilst this is going on, I have another application that is trying to
insert
rows into the table. Normally, the inserts happen straight away, but when
the reader is open each insert takes a very long time to complete.

I realise that this is not an unreasonable thing to happen, given that I
am
trying to write to the table whilst reading from it, but the rows being
written will never be included in the WHERE clause in my select
statement,
and even if they were (which they won't), I wouldn't want them included
in
the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[Charles Law]

Hi Cor

No, I'm not explicitly using transaction locking. I thought, therefore, that
the reader would use row level locking, but if it is, it is still causing
some kind of locking problem.

Charles
"Cor Ligthert[MVP]" <no************ @planet.nlwrote in message
news:1E******** *************** ***********@mic rosoft.com...

Charles,

You are by the way not using transaction locking, because then this is the
normal behaviour.

Cor

"Charles Law" <bl***@nowhere. comschreef in bericht
news:Om******** ******@TK2MSFTN GP06.phx.gbl...

>>I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through
the rows, writing them out to a file. This takes about 5 minutes until I
close the reader.

Whilst this is going on, I have another application that is trying to
insert rows into the table. Normally, the inserts happen straight away,
but when the reader is open each insert takes a very long time to
complete.

I realise that this is not an unreasonable thing to happen, given that I
am trying to write to the table whilst reading from it, but the rows
being written will never be included in the WHERE clause in my select
statement, and even if they were (which they won't), I wouldn't want them
included in the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[Charles Law]

Hi Jack

I did read up about this, but it suggested that the default is row level
locking, which seemed to be the one I'd want anyway, so I haven't attempted
to change it. I have just looked again, and I see there is more to this than
I first thought, so I will read up.

Cheers

Charles
"Jack Jackson" <jj******@cinno vations.netwrot e in message
news:55******** *************** *********@4ax.c om...

On Thu, 19 Jun 2008 02:17:57 +0100, "Charles Law" <bl***@nowhere. com>
wrote:

>>I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through
the
rows, writing them out to a file. This takes about 5 minutes until I close
the reader.

Whilst this is going on, I have another application that is trying to
insert
rows into the table. Normally, the inserts happen straight away, but when
the reader is open each insert takes a very long time to complete.

I realise that this is not an unreasonable thing to happen, given that I
am
trying to write to the table whilst reading from it, but the rows being
written will never be included in the WHERE clause in my select statement,
and even if they were (which they won't), I wouldn't want them included in
the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

You might take a look at the Transact-SQL statement SET TRANSACTION
ISOLATION LEVEL.

[Charles Law]

Hi Tibor

Thanks for the reply. I hadn't thought about the indexing issue. I will add
these to my reading list.

Cheers

Charles
"Tibor Karaszi" <ti************ *************** @hotmail.nomail .comwrote in
message news:FC******** *************** ***********@mic rosoft.com...

If the SELECT limits itself using a WHERE clause to rows which aren't in
the inserted set, then you have a chance to have the SELECT not blocked by
your INSERTs. But that also depends on what execution plan you get. If SQL
Server drive the SELECT using an index which is on something that can be
used to exclude the rows to INSERT then you shouldn't see this blocking.
However, considering you return so many rows, you need to carefully
evaluate your indexing strategy as well as your SELECT query to make this
happen.

Other options include Snapshot isolation and the READPAST optimizer hint.
Those are well documented in Books Online.

--
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://sqlblog.com/blogs/tibor_karaszi
"Charles Law" <bl***@nowhere. comwrote in message
news:Om******** ******@TK2MSFTN GP06.phx.gbl...

>>I have a sproc that returns data from a table using a simple SELECT. There
are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate through
the rows, writing them out to a file. This takes about 5 minutes until I
close the reader.

Whilst this is going on, I have another application that is trying to
insert rows into the table. Normally, the inserts happen straight away,
but when the reader is open each insert takes a very long time to
complete.

I realise that this is not an unreasonable thing to happen, given that I
am trying to write to the table whilst reading from it, but the rows
being written will never be included in the WHERE clause in my select
statement, and even if they were (which they won't), I wouldn't want them
included in the selected rows.

Is there a way to read rows so that inserts can still occur without
blocking?

I am using VB.NET in VS2005, and SQL Server 2005.

TIA

Charles

[Andrew Morton]

Charles Law wrote:

I have a sproc that returns data from a table using a simple SELECT.
There are quite a few rows returned, e.g. ~150,000.

In my first application, I use a reader on the sproc and iterate
through the rows, writing them out to a file. This takes about 5
minutes until I close the reader.

If you are doing

while moreRecords
begin
read record
write record to file
end

then maybe the writing to disk is the slow step, so how about

while moreRecords
begin
read record
append record to stringbuilder
end
write stringbuilder to file

?

I take it getting the sp to write to a file is not an option?

Andrew