I have been writing or reviewing codes in
Salesforce for over six years now. Whenever one comes across a tricky situation
which involves processing huge volumes of data “Batch Apex” is the way to go,
but every now and then you may be alarmed by someone telling you – that hey I
hit the 10k limit while executing a Batch Job!
You would wonder- how is that possible?
Soon you would realize that its the result of one the common slips that one
does while designing a “Batch Job”. Most commonly we fetch records in access of 10,000 within the Execute() method. Treat all code written within execute() method as if you are writing for normal Apex.
Batch Apex surely has more flexible
Governor Limits for example:-
·
200 SOQL per cycle (Please check the latest limit
a s per latest release)
·
Records retrieved by SOQL query
50,000,000 as against 50k in the normal apex.
·
Heap Size is much larger than
that compared to normal apex.
Why
Batch Job is capable of handling huge data sets?
One
has to understand what makes Batch Apex successful in processing huge data
sets:-
·
The large data set is processed
in batches – which implies that the parameter “query” in Start Method () that has to be the query which
will return the bulk of data. Please refer to following code snippet for
clarity:-
global Database.QueryLocator start(Database.BatchableContext BC){
global Database.QueryLocator start(Database.BatchableContext BC){
return Database.getQueryLocator(query);
Common Pitfalls
è You might say well what’s new
in that we all know that. Well true but just reiterating -that the dataset
which is the largest - it has to be fetched with the SOQL in “Query” and then
processed in batches
è Always remember within the
Execute() method never execute an Insert or update which will process more that
10k records in a cycle.
·
Also the enhanced governor
limits enables the Batch Apex to process huge datasets, but one needs to
cautious that though relaxed the governor still exist w.r.t. Batch Apex too.
The following may be important for considering while finalizing your design and
organization wide setup:-
o
Batch Apex Governor Limits
o
These are the governor Limits
you need to keep in mind when dealing with Batch Apex
o
Up to five queued or active
batch jobs are allowed for Apex.
o
A user can have up to 50 query
cursors open at a time. For example, if 50 cursors are open and a client
application still logged in as the same user attempts to open a new one, the
oldest of the 50 cursors is released. Note that this limit is different for the
batch Apex start method, which can have up to five query cursors open at a time
per user. The other batch Apex methods have the higher limit of 50 cursors.
Cursor limits for different Force.com features are tracked separately. For
example, you can have 50 Apex query cursors, 50 batch cursors, and 50
Visualforce cursors open at the same time.
o
A maximum of 50 million records
can be returned in the Database.QueryLocator object. If more than 50 million
records are returned, the batch job is immediately terminated and marked as
Failed. So if you have a requirement to process in excess of that value factor
in the necessary checks and balances in your design.
o
If the start method returns a
QueryLocator, the optional scope parameter of Database.executeBatch can have a
maximum value of 2,000. If you set to a higher value it will anyways break it
into smaller chunks, which is a blessing in a sense.
o
If no size is specified with
the optional scope parameter of Database.executeBatch, Salesforce chunks the
records returned by the start method into batches of 200, and then passes each
batch to the execute method. Apex governor limits are reset for each execution
of execute.
o
The start, execute, and finish
methods can implement up to 10 callouts each.
o
Batch executions are limited to
10 callouts per method execution.
o
The maximum number of batch
executions is 250,000 per 24 hours.
o
Only one batch Apex job's start
method can run at a time in an organization. Batch jobs that haven’t started
yet remain in the queue until they're started. Note that this limit doesn't
cause any batch job to fail and execute methods of batch Apex jobs still run in
parallel if more than one job is running.
