[SOLVED] Execute MongoTemplate.aggregate without row retrival

Execute MongoTemplate.aggregate without row retrival

I'm using the Spring Mongo driver to execute a large mongo aggregation statement that will run for a period of time. The output stage of this aggregation writes the output of the aggregation into a new collection. At no point do I need to retrieve the results of this aggregation in-memory.

When I run this in Spring boot, the JVM is running out of memory doing row retrieval, although I'm not using or storing any of the results.

Is there a way to skip row retrieval using MongoTemplate.aggregate?

Ex:

mongoTemplate.aggregate(Aggregation.newAggregation(
   Aggregation.sort(new Sort(new Sort.Order(Sort.Direction.DESC, "createdOn"))),

   Aggregation.group("accountId")
      .first("bal").as("bal")
      .first("timestamp").as("effectiveTimestamp"),

   Aggregation.project("_id", "effectiveTimestamp")
                        .andExpression("trunc(bal * 10000 + 0.5) / 100").as("bal"),

   aggregationOperationContext -> new Document("$addFields", new Document("history",Arrays.asList(historyObj))),

   // Write results out to a new collection - Do not store in memory
   Aggregation.out("newBalance")
).withOptions(Aggregation.newAggregationOptions().allowDiskUse(true).build()),
   "account", Object.class
);

Solution

I was able to resolve this by using

MongoTempalte.aggregateStream(...).withOptions(Aggregation.newAggregationOptions().cursorBatchSize(0).build)