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From <robert.kasani...@accenture.com>
Subject RE: how to map huge resultsets?
Date Thu, 04 Oct 2007 13:43:03 GMT
Thanks for the insights Jeff.

 

Shifting a paradigm and letting iBATIS control the flow is not an option
this case, but I think iBATIS can still be used in a slightly different
"driving query" scenario. In this case a "driving query" is run first
which retrieves all primary keys. When framework asks for next item, the
item provider takes the next key and asks iBATIS for the corresponding
object - it is not what I was originally looking for, but still useful.

 

Btw. the motivation for my post is to figure out how ibatis can be
integrated as an input source for the emerging Spring-Batch framework.
It provides support for ordinary sql with manual mapping, but supporting
ORM frameworks (especially Hibernate & iBATIS) would be a valuable
addition.

 

Robert

 

________________________________

From: Jeff Butler [mailto:jeffgbutler@gmail.com] 
Sent: Thursday, October 04, 2007 14:15
To: user-java@ibatis.apache.org
Subject: Re: how to map huge resultsets?

 

Your question is not that confusing.  Here are the answers:

 

1. No (although the approach suggested by Christopher Lamey is very
close if you are willing to shift your paradigm)

 

2. If the result set is truly huge, then approach #1 is a bad idea
because iBATIS will have to read through huge amounts of data to get to
the latter parts of the result set in subsequent calls (this is why
Larry asked about selecting by primary key rather than returning such a
huge result set) 

 

I guess you'll have to stick with Hibernate :)

 

Jeff Butler

 

On 10/4/07, robert.kasanicky@accenture.com
<robert.kasanicky@accenture.com > wrote: 

Seems like my question was quite confusing, so I'll try to explain what
I need once again from scratch. 

1. I need to process a potentially huge number of rows (so
queryForList(query) is not an option because it would try to load all
objects into memory at once).

2. I need to control the iteration over the query results, so I can't 
use queryWithRowHandler (in this case iBATIS iterates and I only tell
iBATIS how each record should be processed - I need to be able to ask
iBATIS for the next record instead - it is the internal vs. external
iterator difference, or SAX vs. StAX in case of XML processing or how
collections are typically iterated in ruby/groovy vs. Java or ... you
name it). Simply framework iterates, iBATIS knows the query and must
provide next record when it is asked for it. 

First approach:
It is possible to implement these requirements by using
queryForList(query, skipSize, maxSize) and  query the database
TOTAL_ROW_COUNT / maxSize times (issuing a new query when records from 
current list have been processed - this is invisible to the user
(framework) who just iteratively asks for next record for processing).

Second approach:
Hibernate allows to get a ScrollableResults object for a query allowing 
the user to move the cursor and ask for an object that corresponds to
the current row.

Questions:
1. is the second approach possible with iBATIS?
2. first vs. second approach pros & cons?

Thanks 
Robert

-----Original Message-----
From: larry.meadors@gmail.com [mailto:larry.meadors@gmail.com] On Behalf
Of Larry Meadors 
Sent: Thursday, October 04, 2007 01:18
To: user-java@ibatis.apache.org
Subject: Re: how to map huge resultsets?

I'm confused, how would grabbing chunks of a huge result set be more 
efficient than grabbing the records by PK?

Couldn't you just have a select that grabbed the requested item, and
passed it back to the consumer?

Larry


On 10/3/07, robert.kasanicky@accenture.com
<robert.kasanicky@accenture.com> wrote:
> My problem with RowHandler is that iBATIS controls the iteration. I
just say 
>
> sqlMap.queryWithRowHandler ("getAllItems", rowHandler);
>
> and all items get processed by the rowHandler.
>
> But in my case I need to make iBATIS return items one-by-one when it 
is asked to do so because the framework controls the iteration.
> This is a very simplified basic logic of the framework:
>
> while (itemProvider.hasNext()) {
>  Object item = itemProvider.next ();
>  process(item);
> }
>
>
>
> -----Original Message-----
> From: Christopher Lamey [mailto:clamey@localmatters.com]
> Sent: Wed 10/3/2007 11:55 PM 
> To: user-java@ibatis.apache.org
> Subject: Re: how to map huge resultsets?
>
> Hmm...I don't see how having an external framework prevents you from 
using a
> RowHandler.  Your item provider could implement the RowHandler
interface and
> the external code wouldn't know or care about it.  Or your item
provider
> could wrap something that does implement RowHandler so the external 
code
> doesn't know it exists.  The main point is that you can pull mapped
objects
> on a row by row basis from the database.
>
> How is a RowHandler different that what you were describing in your 
first
> mail?
>
> On 10/3/07 3:33 PM, "robert.kasanicky@accenture.com"
> <robert.kasanicky@accenture.com > wrote:
>
> >
> > Thanks for your reply.
> >
> > I can't use the rowhandler callback because the iteration is
external to
> > iBATIS. In my case a batch framework iteratively asks for an item 
and
> > processes it - and I am trying to implement an iBATIS item provider
(I realize
> > now I should have explained this in the initial post).
> >
> > Robert
> >
> > 
> > -----Original Message-----
> > From: Christopher Lamey [mailto:clamey@localmatters.com]
> > Sent: Wed 10/3/2007 11:06 PM
> > To: user-java@ibatis.apache.org
> > Subject: Re: how to map huge resultsets?
> >
> > Hello,
> >
> > You should take a look at the RowHandler interface and the
> > queryWithRowHandler calls in SqlMapClient (page 61 of the pdf). 
Basically,
> > the RowHandler gets invoked for every row returned rather than
mapping all
> > the rows into objects in a collection.
> >
> > Cheers,
> > Chris
> > 
> >
> > On 10/3/07 2:37 PM, "robert.kasanicky@accenture.com"
> > <robert.kasanicky@accenture.com > wrote:
> >
> >> Hello,
> >>
> >> I am wondering whether it possible to implement the following
scenario with
> >> iBATIS:
> >>
> >>    1. run an iBATIS-managed select 
> >>    2. get a scrollable result set instead of a list of mapped
objects
> >>    3. manually scroll the result set and ask iBATIS for object
corresponding
> >> to current row
> >>
> >> Hibernate provides this possibility
> >> (http://www.hibernate.org/hib_docs/reference/en/html/batch.html )
so
I thought
> >> it would be feasible with iBATIS too, but I couldn't figure out a
way. The
> >> motivation is a batch scenario where the select returns a huge
number of rows
> >> so all mapped objects can't be loaded into memory at once. 
> >>
> >> The iBATIS way I am aware of is to use queryForList(String
statementName, int
> >> skipResults, int maxResults), but this means querying the database
> >> (TOTAL_NUMBER_OF_ROWS / maxResults) times. 
> >>
> >> Can somebody give advice about pros & cons of the two approaches?
> >>
> >> Thanks
> >> Robert
> >>
> >>
> >> This message is for the designated recipient only and may contain 
privileged,
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> >
> >
> >
> >
> > This message is for the designated recipient only and may contain
privileged,
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it in
> > error, please notify the sender immediately and delete the original.
Any
> > other use of the email by you is prohibited.
>
>
>
>
> This message is for the designated recipient only and may contain 
privileged, proprietary, or otherwise private information.  If you have
received it in error, please notify the sender immediately and delete
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> 
>


This message is for the designated recipient only and may contain
privileged, proprietary, or otherwise private information.  If you have
received it in error, please notify the sender immediately and delete
the original.  Any other use of the email by you is prohibited. 

 



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