With this post I'm starting to prepare for our UKOUG'13 conference sessions. You can attend two of our sessions on UKOUG'13 Super Sunday, December 1st. These sessions are scheduled to run immediately one after another, so we are going to have two straight hours to discuss topics around ADF - ADF Anti-Patterns: Dangerous Tutorials, ADF Development Survival Kit. You should stop by to say hi, me and my colleague Florin Marcus, will be happy to answer any technical question about ADF.
Today post topic will be covered in the first session - ADF Anti-Patterns: Dangerous Tutorials. If you know how to implement CRUD functionality, you might be surprised - there are more things to know. I will describe one issue specifically related to ADF 12c, in the next post will present scenario reproduced in ADF 11g.
In your production application, you may experience WebLogic Stuck Threads. This is usually related to the large fetching, in most cases it happens unexpected and is not reproduced easily. In ADF 11g this is related to AM passivation/activation behaviour (will be described more in the next post), in ADF 12c I found another reason for unexpected large fetch in CRUD - ChangeEventPolicy = PPR setting usage for ADF iterator in Page Definition.
Here you can download fixed CRUD application for ADF 12c - LargeFetchApp.zip. This applications provides to methods, to insert 10000 rows into Regions table and remove the same rows. This is important to reproduce the error - it is easily reproduced when there are more records in the DB. Run populateTable method to insert 10000 rows into Regions table:
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After running populateTable method, around 10000 rows should be available in the DB:
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Regions VO implementation class contains overridden method for createRowFromResultSet. This method tracks every row fetched through this VO and reports it to the log:
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Double check Regions iterator properties in Page Definition:
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You will see ChangeEventPolicy = ppr, is set by default:
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Run test application (make sure ChangeEventPolicy = ppr), press Create button - you will experience 15 to 30 seconds delay, before blank row will show up:
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This is easily reproduced, if table is large enough (for example 10000 rows or more), as it was generated with populateTable method. To see ADF log output for Regions VO implementation class, make sure to set FINEST level in ADF logger config:
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You will see lots of rows fetched during CreateInsert operation invocation, around 40000 rows fetched (means duplicates, as there are 10000 rows only in the table). This explains why Create is so slow, and this is by default in ADF 12c. It makes so many findByKey method calls:
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In production system, when multiple users are doing same operation and even more data in the table - this generates Stuck Threads on WebLogic server and finally application stops. Simply because it consumes too much memory to create huge rowsets for all the data fetched from the DB.
You should change ChangeEventPolicy = none, this prevents unexpected large fetch on CreateInsert:
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New row will be inserted instantly:
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General recommendation - you should avoid using default setting for ChangeEventPolicy = ppr, it creates too many side effects usually. Seems like this functionality is not well tested yet.
Today post topic will be covered in the first session - ADF Anti-Patterns: Dangerous Tutorials. If you know how to implement CRUD functionality, you might be surprised - there are more things to know. I will describe one issue specifically related to ADF 12c, in the next post will present scenario reproduced in ADF 11g.
In your production application, you may experience WebLogic Stuck Threads. This is usually related to the large fetching, in most cases it happens unexpected and is not reproduced easily. In ADF 11g this is related to AM passivation/activation behaviour (will be described more in the next post), in ADF 12c I found another reason for unexpected large fetch in CRUD - ChangeEventPolicy = PPR setting usage for ADF iterator in Page Definition.
Here you can download fixed CRUD application for ADF 12c - LargeFetchApp.zip. This applications provides to methods, to insert 10000 rows into Regions table and remove the same rows. This is important to reproduce the error - it is easily reproduced when there are more records in the DB. Run populateTable method to insert 10000 rows into Regions table:
After running populateTable method, around 10000 rows should be available in the DB:
Regions VO implementation class contains overridden method for createRowFromResultSet. This method tracks every row fetched through this VO and reports it to the log:
Double check Regions iterator properties in Page Definition:
You will see ChangeEventPolicy = ppr, is set by default:
Run test application (make sure ChangeEventPolicy = ppr), press Create button - you will experience 15 to 30 seconds delay, before blank row will show up:
This is easily reproduced, if table is large enough (for example 10000 rows or more), as it was generated with populateTable method. To see ADF log output for Regions VO implementation class, make sure to set FINEST level in ADF logger config:
You will see lots of rows fetched during CreateInsert operation invocation, around 40000 rows fetched (means duplicates, as there are 10000 rows only in the table). This explains why Create is so slow, and this is by default in ADF 12c. It makes so many findByKey method calls:
In production system, when multiple users are doing same operation and even more data in the table - this generates Stuck Threads on WebLogic server and finally application stops. Simply because it consumes too much memory to create huge rowsets for all the data fetched from the DB.
You should change ChangeEventPolicy = none, this prevents unexpected large fetch on CreateInsert:
New row will be inserted instantly:
General recommendation - you should avoid using default setting for ChangeEventPolicy = ppr, it creates too many side effects usually. Seems like this functionality is not well tested yet.