How to use Cadence/Temporal versioning API( workflow.getVersion) in a loop - cadence-workflow

Question

Imagine this workflow of 10 activities in a loop:
public class LoopWorkflowImpl implements LoopWorkflow{
private final Api api = Workflow.newActivityStub(Api.class, ...)
#override
public int start(){
int sum = 0;
for(int i=0; i<10; i++){
sum += api.getCount();
}
return sum;
}
}
How can I change api.getCount() to api.getCountV2() for existing workflows?
E.g. if there is workflow already completed 5 activities with api.getCount(), how can let let it use api.getCountV2() for the rest 5 activities?

Answer 1

Correct Way to apply new behavior for old and new workflow
This is what you should do -- using the versioning API with changeId for each iteration:
public class LoopWorkflowImpl implements LoopWorkflow{
private final Api api = Workflow.newActivityStub(Api.class, ...)
#override
public int start(){
int sum = 0;
for(int i=0; i<10; i++){
int version = Workflow.getVersion("useV2API"+i, Workflow.DEFAULT_VERSION, 1)
if( version == 1){
sum += api.getCountV2();
}else{
sum += api.getCount();
}
}
return sum;
}
}
Below will only apply for new workflows
Many people will do this instead and it won't work for the existing workflow
public class LoopWorkflowImpl implements LoopWorkflow{
private final Api api = Workflow.newActivityStub(Api.class, ...)
#override
public int start(){
int sum = 0;
for(int i=0; i<10; i++){
int version = Workflow.getVersion("useV2API", Workflow.DEFAULT_VERSION, 1)
if( version == 1){
sum += api.getCountV2();
}else{
sum += api.getCount();
}
}
return sum;
}
}
Why
This is because of an important contract of Workflow.getVersion() API --
The return value from the API for the same changeId is immutable once returned. This is guaranteed with or without the version is being written into history using MarkerRecord event.
So in the 2nd solution , on the first iteration, Workflow.getVersion() will returns Workflow.DEFAULT_VERSION(-1) as there is no version marker during replay. So in the rest iteration, it will always return Workflow.DEFAULT_VERSION.
The best way to fix is to include the iteration Id into the changeId. Using the different changeId will allow the versioning to pick different version for different iteration.
If you are worried about this will create too many version marker events in the history, you can combine this solution with the global versioning pattern to only do this for old workflows:
public class LoopWorkflowImpl implements LoopWorkflow{
private final Api api = Workflow.newActivityStub(Api.class, ...)
private GlovalVersionProvider globalVersionProvider = GlobalVersionProvider.get();
#override
public int start(){
if (globalVersionProvider.isAfterVersionOfUsingGlobalVersion()) {
GlobalVersionProvider.upsertGlobalVersionSearchAttribute();
}
int sum = 0;
for(int i=0; i<10; i++){
if (globalVersionProvider.isAfterVersionOfUsingV2Api()) {
sum += api.getCountV2();
}else{
int version = Workflow.getVersion("useV2API"+i, Workflow.DEFAULT_VERSION, 1)
if( version == 1){
sum += api.getCountV2();
}else{
sum += api.getCount();
}
}
}
return sum;
}
}
So the the versioning marker with iteration index is only applying for existing old workflow executions.