Error when loading form with a!queryEntity

Question

We have SAIL Form which takes inputs from user and query database using a!queryEntity, passing those inputs. We are facing issue, sometimes we receive error pop-up on UI when user enters details to fetch data from database, but sometimes database transaction is successful. When we checked logs- "com.appiancorp.process.expression.ExpressionRuntimeException$AppianExceptionWithRootCauseProvider: Expression evaluation error in rule 'prequal_cpe_create_device_search' (called by rule 'Show_User_data_UI') at function a!buttonWidget [line 76]: An error occurred while executing a save: Expression evaluation error in rule 'Fetch_User_Data_From_Database' at function a!queryEntity: An error occurred while retrieving the data. (APNX-1-4198-019) ./server.log.2016-04-18:18:45:16,285 INFO [stdout] (ajp-/144.226.143.101:8009-26) Caused by: com.appiancorp.suiteapi.common.exceptions.AppianException: An error occurred while executing a save: Expression e... 
 OriginalPostID-207641 
 OriginalPostID-207641

akshayan · Accepted Answer

Check if you are exceeding limit. Queries that result in more than 1MB of application server memory usage, by default, are canceled.
Queries that take longer than 10 seconds are also, by default, canceled.
See forum.appian.com/.../Configuring_Relational_Databases.html

Durgesh · Answer

I think, this issue falls under the research and more investigation.

There could be many reasons for this error. Request taking long time to fetch the data, connection failure to the db server, run-time interruption to the incoming request and so on.

As you have mentioned, it happens sometimes. Can you check and try to compare both the scenario when it happens and when not?

Adding to this, my suggestions would be -
1) Check if db table is properly indexed
2) Views created with less complex logic and gives good response without delay every time.
3) Any db query if taking more time to execute, needs to be re-evaluated.

Please let us know your findings and research. It would be helpful for us as well.