[MarkLogic Dev General] Try catch in xquery

[Abishek N]

What are the pointers while exception handling in ml? One of the pointers
we have already heard is
"Reduce the use of try/catch where applicable. This is especially true in
situations where try/catch blocks may be nested. Try/catch blocks have a
negative impact on performance due to the fact that the block must be
completely evaluated before the server can move on. "

So does this mean that we have to avoid having try catch blocks around lots
of lines of code? and try to keep the try catch block as short as
possible..
So in the eg. below statement 3 try catch block would not be triggered until
the statement 1 and statement 2 get executed, is that correct? Since
statement 2 is outside try catches there is a possibility it could get lazy
evaluated.

try {
statement 1
}
catch{
}

statement 2

try {
statement 3
}
catch{
}

Similarly in the below scenario.. if we have nested try catches like
below... statement 5 would not get executed until statement 1,2,3 get
executed.. however statement 4 could get executed..
try {

try
{
statement 1
}
catch{
}

statement 2

try {
statement 3
}
catch{
}

}

statement 4

try {
statement 5
}
catch{
}

Please confirm if our understanding is correct.

Regards Abishek
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[Geert Josten]

Hi Abishek,

What is meant with 'reduce the use of try/catch' is that you should make sensible use of try/catch and manually throwing exceptions using the error function. Exception handling is (relatively) slow in most languages, so if you have the option to prevent a throw and a catch by simply using an extra if, then do so. On other occasions, you might want to be sure certain statements are always executed, or that certain actions are taken when an exception is thrown.

A good example is trying to connect to an external resource using xdmp:http-get. If it fails with a timeout, it throws an exception. It is not uncommon to put a try catch around it and connect to a different resource, or return some default value instead.

Personally, I don't bother about try/catch performance too much. Just use them sensibly..

Kind regards,
Geert

Van: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] Namens Abishek N
Verzonden: donderdag 5 mei 2011 19:05
Aan: General MarkLogic Developer Discussion
Onderwerp: [MarkLogic Dev General] Try catch in xquery

What are the pointers while exception handling in ml? One of the pointers we have already heard is
"Reduce the use of try/catch where applicable. This is especially true in situations where try/catch blocks may be nested. Try/catch blocks have a negative impact on performance due to the fact that the block must be completely evaluated before the server can move on. "

So does this mean that we have to avoid having try catch blocks around lots of lines of code? and try to keep the try catch block as short as possible..
So in the eg. below statement 3 try catch block would not be triggered until the statement 1 and statement 2 get executed, is that correct? Since statement 2 is outside try catches there is a possibility it could get lazy evaluated.

try {
statement 1
}
catch{
}

statement 2

try {
statement 3
}
catch{
}

Similarly in the below scenario.. if we have nested try catches like below... statement 5 would not get executed until statement 1,2,3 get executed.. however statement 4 could get executed..
try {
try
{
statement 1
}
catch{
}

statement 2

try {
statement 3
}
catch{
}

}

statement 4

try {
statement 5
}
catch{
}

Please confirm if our understanding is correct.

Regards Abishek
-------------- next part --------------
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[Abishek N]

Thanks Geert for your response.. I agree with you on those lines., that's
the default way we handle exception scenarios in other programming
languages. The question around the try catch block is more with respect to
the impact on parallel processing and lazy evaluations which is applicable
for ML ..

On Thu, May 5, 2011 at 1:46 PM, Geert Josten <geert.josten at daidalos.nl>wrote:

> Hi Abishek,
>
>
>
> What is meant with ?reduce the use of try/catch? is that you should make
> sensible use of try/catch and manually throwing exceptions using the error
> function. Exception handling is (relatively) slow in most languages, so if
> you have the option to prevent a throw and a catch by simply using an extra
> if, then do so. On other occasions, you might want to be sure certain
> statements are always executed, or that certain actions are taken when an
> exception is thrown.
>
>
>
> A good example is trying to connect to an external resource using
> xdmp:http-get. If it fails with a timeout, it throws an exception. It is not
> uncommon to put a try catch around it and connect to a different resource,
> or return some default value instead.
>
>
>
> Personally, I don?t bother about try/catch performance too much. Just use
> them sensibly..
>
>
>
> Kind regards,
>
> Geert
>
>
>
> *Van:* general-bounces at developer.marklogic.com [mailto:
> general-bounces at developer.marklogic.com] *Namens *Abishek N
> *Verzonden:* donderdag 5 mei 2011 19:05
> *Aan:* General MarkLogic Developer Discussion
> *Onderwerp:* [MarkLogic Dev General] Try catch in xquery
>
>
>
> What are the pointers while exception handling in ml? One of the pointers
> we have already heard is
> "Reduce the use of try/catch where applicable. This is especially true in
> situations where try/catch blocks may be nested. Try/catch blocks have a
> negative impact on performance due to the fact that the block must be
> completely evaluated before the server can move on. "
>
> So does this mean that we have to avoid having try catch blocks around
> lots of lines of code? and try to keep the try catch block as short as
> possible..
> So in the eg. below statement 3 try catch block would not be triggered
> until the statement 1 and statement 2 get executed, is that correct? Since
> statement 2 is outside try catches there is a possibility it could get lazy
> evaluated.
>
> try {
> statement 1
> }
> catch{
> }
>
> statement 2
>
> try {
> statement 3
> }
> catch{
> }
>
> Similarly in the below scenario.. if we have nested try catches like
> below... statement 5 would not get executed until statement 1,2,3 get
> executed.. however statement 4 could get executed..
> try {
>
> try
> {
> statement 1
> }
> catch{
> }
>
> statement 2
>
> try {
> statement 3
> }
> catch{
> }
>
>
> }
>
> statement 4
>
> try {
> statement 5
> }
> catch{
> }
>
> Please confirm if our understanding is correct.
>
> Regards Abishek
>
> _______________________________________________
> General mailing list
> General at developer.marklogic.com
> http://developer.marklogic.com/mailman/listinfo/general
>
>


--
Regards Abishek
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[Geert Josten]

Hi Abishek,

You were probably triggered by the phrase 'the block must be completely evaluated before the server can move on'. I'm not familiar with the internals of MarkLogic Server, but there is nothing against processing the contents of the try block in parallel threads (provided the code in the block is suitable for it)..

In the end there is only one real way to know what makes true difference: measure it. I recommend writing some real scenario's and run them against MarkLogic Server using performance-meters. (http://developer.marklogic.com/code/performance-meters)

Kind regards,
Geert

Van: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] Namens Abishek N
Verzonden: donderdag 5 mei 2011 20:34
Aan: General MarkLogic Developer Discussion
Onderwerp: Re: [MarkLogic Dev General] Try catch in xquery

Thanks Geert for your response.. I agree with you on those lines., that's the default way we handle exception scenarios in other programming languages. The question around the try catch block is more with respect to the impact on parallel processing and lazy evaluations which is applicable for ML ..
On Thu, May 5, 2011 at 1:46 PM, Geert Josten <geert.josten at daidalos.nl<mailto:geert.josten at daidalos.nl>> wrote:
Hi Abishek,

What is meant with 'reduce the use of try/catch' is that you should make sensible use of try/catch and manually throwing exceptions using the error function. Exception handling is (relatively) slow in most languages, so if you have the option to prevent a throw and a catch by simply using an extra if, then do so. On other occasions, you might want to be sure certain statements are always executed, or that certain actions are taken when an exception is thrown.

A good example is trying to connect to an external resource using xdmp:http-get. If it fails with a timeout, it throws an exception. It is not uncommon to put a try catch around it and connect to a different resource, or return some default value instead.

Personally, I don't bother about try/catch performance too much. Just use them sensibly..

Kind regards,
Geert

Van: general-bounces at developer.marklogic.com<mailto:general-bounces at developer.marklogic.com> [mailto:general-bounces at developer.marklogic.com<mailto:general-bounces at developer.marklogic.com>] Namens Abishek N
Verzonden: donderdag 5 mei 2011 19:05
Aan: General MarkLogic Developer Discussion
Onderwerp: [MarkLogic Dev General] Try catch in xquery

What are the pointers while exception handling in ml? One of the pointers we have already heard is
"Reduce the use of try/catch where applicable. This is especially true in situations where try/catch blocks may be nested. Try/catch blocks have a negative impact on performance due to the fact that the block must be completely evaluated before the server can move on. "

So does this mean that we have to avoid having try catch blocks around lots of lines of code? and try to keep the try catch block as short as possible..
So in the eg. below statement 3 try catch block would not be triggered until the statement 1 and statement 2 get executed, is that correct? Since statement 2 is outside try catches there is a possibility it could get lazy evaluated.

try {
statement 1
}
catch{
}

statement 2

try {
statement 3
}
catch{
}

Similarly in the below scenario.. if we have nested try catches like below... statement 5 would not get executed until statement 1,2,3 get executed.. however statement 4 could get executed..
try {
try
{
statement 1
}
catch{
}

statement 2

try {
statement 3
}
catch{
}

}

statement 4

try {
statement 5
}
catch{
}

Please confirm if our understanding is correct.

Regards Abishek

_______________________________________________
General mailing list
General at developer.marklogic.com<mailto:General at developer.marklogic.com>
http://developer.marklogic.com/mailman/listinfo/general



--
Regards Abishek
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[Jason Hunter]

If there's any background executions happening inside the try block (a cts:element-values call for example, or an xdmp:http-get) they have to be finished before exiting the try block. Because if they error out, the error has to be handled in the catch.

Geert's advice is spot-on. Write the appropriate code for your needs. This is pretty advanced stuff that you shouldn't have to worry about except in rare circumstances.

(What's pretty cool is how much background thread execution is happening without you ever realizing it.)

-jh-

On May 5, 2011, at 12:34 PM, Geert Josten wrote:

> Hi Abishek,
>
> You were probably triggered by the phrase ?the block must be completely evaluated before the server can move on?. I?m not familiar with the internals of MarkLogic Server, but there is nothing against processing the contents of the try block in parallel threads (provided the code in the block is suitable for it)..
>
> In the end there is only one real way to know what makes true difference: measure it. I recommend writing some real scenario?s and run them against MarkLogic Server using performance-meters. (http://developer.marklogic.com/code/performance-meters)
>
> Kind regards,
> Geert
>
> Van: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] Namens Abishek N
> Verzonden: donderdag 5 mei 2011 20:34
> Aan: General MarkLogic Developer Discussion
> Onderwerp: Re: [MarkLogic Dev General] Try catch in xquery
>
> Thanks Geert for your response.. I agree with you on those lines., that's the default way we handle exception scenarios in other programming languages. The question around the try catch block is more with respect to the impact on parallel processing and lazy evaluations which is applicable for ML ..
>
> On Thu, May 5, 2011 at 1:46 PM, Geert Josten <geert.josten at daidalos.nl> wrote:
> Hi Abishek,
>
> What is meant with ?reduce the use of try/catch? is that you should make sensible use of try/catch and manually throwing exceptions using the error function. Exception handling is (relatively) slow in most languages, so if you have the option to prevent a throw and a catch by simply using an extra if, then do so. On other occasions, you might want to be sure certain statements are always executed, or that certain actions are taken when an exception is thrown.
>
> A good example is trying to connect to an external resource using xdmp:http-get. If it fails with a timeout, it throws an exception. It is not uncommon to put a try catch around it and connect to a different resource, or return some default value instead.
>
> Personally, I don?t bother about try/catch performance too much. Just use them sensibly..
>
> Kind regards,
> Geert
>
> Van: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] Namens Abishek N
> Verzonden: donderdag 5 mei 2011 19:05
> Aan: General MarkLogic Developer Discussion
> Onderwerp: [MarkLogic Dev General] Try catch in xquery
>
> What are the pointers while exception handling in ml? One of the pointers we have already heard is
> "Reduce the use of try/catch where applicable. This is especially true in situations where try/catch blocks may be nested. Try/catch blocks have a negative impact on performance due to the fact that the block must be completely evaluated before the server can move on. "
>
> So does this mean that we have to avoid having try catch blocks around lots of lines of code? and try to keep the try catch block as short as possible..
> So in the eg. below statement 3 try catch block would not be triggered until the statement 1 and statement 2 get executed, is that correct? Since statement 2 is outside try catches there is a possibility it could get lazy evaluated.
>
> try {
> statement 1
> }
> catch{
> }
>
> statement 2
>
> try {
> statement 3
> }
> catch{
> }
>
> Similarly in the below scenario.. if we have nested try catches like below... statement 5 would not get executed until statement 1,2,3 get executed.. however statement 4 could get executed..
> try {
>
> try
> {
> statement 1
> }
> catch{
> }
>
> statement 2
>
> try {
> statement 3
> }
> catch{
> }
>
> }
>
> statement 4
>
> try {
> statement 5
> }
> catch{
> }
>
> Please confirm if our understanding is correct.
>
> Regards Abishek
>
> _______________________________________________
> General mailing list
> General at developer.marklogic.com
> http://developer.marklogic.com/mailman/listinfo/general
>
>
>
>
> --
> Regards Abishek
> _______________________________________________
> General mailing list
> General at developer.marklogic.com
> http://developer.marklogic.com/mailman/listinfo/general

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[Abishek N]

Thanks for your response Jason and Geert.. I think the underlying point is
to use try catches judiciously and then think about performance by using
query meter.

On Fri, May 6, 2011 at 12:11 AM, Jason Hunter <jhunter at marklogic.com> wrote:

> If there's any background executions happening inside the try block (a
> cts:element-values call for example, or an xdmp:http-get) they have to be
> finished before exiting the try block. Because if they error out, the error
> has to be handled in the catch.
>
> Geert's advice is spot-on. Write the appropriate code for your needs.
> This is pretty advanced stuff that you shouldn't have to worry about except
> in rare circumstances.
>
> (What's pretty cool is how much background thread execution is happening
> without you ever realizing it.)
>
> -jh-
>
> On May 5, 2011, at 12:34 PM, Geert Josten wrote:
>
> Hi Abishek,
>
> You were probably triggered by the phrase ?the block must be completely
> evaluated before the server can move on?. I?m not familiar with the
> internals of MarkLogic Server, but there is nothing against processing the
> contents of the try block in parallel threads (provided the code in the
> block is suitable for it)..
>
> In the end there is only one real way to know what makes true difference:
> measure it. I recommend writing some real scenario?s and run them against
> MarkLogic Server using performance-meters. (
> http://developer.marklogic.com/code/performance-meters)
>
> Kind regards,
> Geert
>
> *Van:* general-bounces at developer.marklogic.com [mailto:
> general-bounces at developer.marklogic.com] *Namens *Abishek N
> *Verzonden:* donderdag 5 mei 2011 20:34
> *Aan:* General MarkLogic Developer Discussion
> *Onderwerp:* Re: [MarkLogic Dev General] Try catch in xquery
>
>
> Thanks Geert for your response.. I agree with you on those lines., that's
> the default way we handle exception scenarios in other programming
> languages. The question around the try catch block is more with respect to
> the impact on parallel processing and lazy evaluations which is applicable
> for ML ..
> On Thu, May 5, 2011 at 1:46 PM, Geert Josten <geert.josten at daidalos.nl>
> wrote:
> Hi Abishek,
>
> What is meant with ?reduce the use of try/catch? is that you should make
> sensible use of try/catch and manually throwing exceptions using the error
> function. Exception handling is (relatively) slow in most languages, so if
> you have the option to prevent a throw and a catch by simply using an extra
> if, then do so. On other occasions, you might want to be sure certain
> statements are always executed, or that certain actions are taken when an
> exception is thrown.
>
> A good example is trying to connect to an external resource using
> xdmp:http-get. If it fails with a timeout, it throws an exception. It is not
> uncommon to put a try catch around it and connect to a different resource,
> or return some default value instead.
>
> Personally, I don?t bother about try/catch performance too much. Just use
> them sensibly..
>
> Kind regards,
> Geert
>
> *Van:* general-bounces at developer.marklogic.com [mailto:
> general-bounces at developer.marklogic.com] *Namens *Abishek N
> *Verzonden:* donderdag 5 mei 2011 19:05
> *Aan:* General MarkLogic Developer Discussion
> *Onderwerp:* [MarkLogic Dev General] Try catch in xquery
>
>
> What are the pointers while exception handling in ml? One of the pointers
> we have already heard is
> "Reduce the use of try/catch where applicable. This is especially true in
> situations where try/catch blocks may be nested. Try/catch blocks have a
> negative impact on performance due to the fact that the block must be
> completely evaluated before the server can move on. "
>
> So does this mean that we have to avoid having try catch blocks around
> lots of lines of code? and try to keep the try catch block as short as
> possible..
> So in the eg. below statement 3 try catch block would not be triggered
> until the statement 1 and statement 2 get executed, is that correct? Since
> statement 2 is outside try catches there is a possibility it could get lazy
> evaluated.
>
> try {
> statement 1
> }
> catch{
> }
>
> statement 2
>
> try {
> statement 3
> }
> catch{
> }
>
> Similarly in the below scenario.. if we have nested try catches like
> below... statement 5 would not get executed until statement 1,2,3 get
> executed.. however statement 4 could get executed..
> try {
> try
> {
> statement 1
> }
> catch{
> }
>
> statement 2
>
> try {
> statement 3
> }
> catch{
> }
>
> }
>
> statement 4
>
> try {
> statement 5
> }
> catch{
> }
>
> Please confirm if our understanding is correct.
>
> Regards Abishek
>
>
> _______________________________________________
> General mailing list
> General at developer.marklogic.com
> http://developer.marklogic.com/mailman/listinfo/general
>
>
>
> --
> Regards Abishek
> _______________________________________________
> General mailing list
> General at developer.marklogic.com
> http://developer.marklogic.com/mailman/listinfo/general
>
>
>
> _______________________________________________
> General mailing list
> General at developer.marklogic.com
> http://developer.marklogic.com/mailman/listinfo/general
>
>


--
Regards Abishek
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[Abhishek53 S]

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[Mary Holstege]

On Thu, 05 May 2011 11:34:21 -0700, Abhishek53 S <abhishek53.s at tcs.com>
wrote:

> Hi All !
>
> Can someone please suggest the way to extract out bookmarks information
> while PDF to XHTML conversion using CPF in Marklogic.
>

The default conversion application extracts the bookmarks from the PDF
into the file toc.xml (under the xxx_parts directory for that PDF file).
That is, given you converted /whatever/foo.pdf after running through
the default PDF conversion application with it
/whatever/foo_pdf_parts/toc.xml
will contain the bookmarks extracted from the PDF.

//Mary