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// Tests that a $merge stage does not force a pipeline to split into a "shards part" and a "merging
// part" if no other stage in the pipeline would force such a split.
(function() {
"use strict";
load("jstests/aggregation/extras/merge_helpers.js"); // For withEachMergeMode.
const st = new ShardingTest({shards: 2, rs: {nodes: 1}});
const mongosDB = st.s.getDB("test_db");
const inColl = mongosDB["inColl"];
// Two different output collections will be sharded by different keys.
const outCollById = mongosDB["outCollById"];
const outCollBySK = mongosDB["outCollBySK"];
st.shardColl(outCollById, {_id: 1}, {_id: 500}, {_id: 500}, mongosDB.getName());
st.shardColl(outCollBySK, {sk: 1}, {sk: 500}, {sk: 500}, mongosDB.getName());
const numDocs = 1000;
function insertData(coll) {
const bulk = coll.initializeUnorderedBulkOp();
for (let i = 0; i < numDocs; i++) {
bulk.insert({_id: i, sk: numDocs - i});
}
assert.commandWorked(bulk.execute());
}
// Shard the input collection.
st.shardColl(inColl, {_id: 1}, {_id: 500}, {_id: 500}, mongosDB.getName());
// Insert some data to the input collection.
insertData(inColl);
function assertMergeRunsOnShards(explain) {
assert(explain.hasOwnProperty("splitPipeline"), tojson(explain));
assert(explain.splitPipeline.hasOwnProperty("shardsPart"), tojson(explain));
assert.eq(
explain.splitPipeline.shardsPart.filter(stage => stage.hasOwnProperty("$merge")).length,
1,
tojson(explain));
assert(explain.splitPipeline.hasOwnProperty("mergerPart"), tojson(explain));
assert.eq([], explain.splitPipeline.mergerPart, tojson(explain));
}
// Test that a simple $merge can run in parallel. Note that we still expect a 'splitPipeline' in
// the explain output, but the merging half should be empty to indicate that the entire thing is
// executing in parallel on the shards.
withEachMergeMode(({whenMatchedMode, whenNotMatchedMode}) => {
assert.commandWorked(outCollById.remove({}));
assert.commandWorked(outCollBySK.remove({}));
let explain = inColl.explain().aggregate([{
$merge: {
into: outCollById.getName(),
whenMatched: whenMatchedMode,
whenNotMatched: whenNotMatchedMode
}
}]);
assertMergeRunsOnShards(explain);
assert.eq(outCollById.find().itcount(), 0);
// We expect the test to succeed for all $merge modes. However, the 'whenNotMatched: fail'
// mode will cause the test to fail if the source collection has a document without a match
// in the target collection. Similarly 'whenNotMatched: discard' will fail the assertion
// below for the expected number of document in target collection. So we populate the target
// collection with the same documents as in the source.
if (whenNotMatchedMode == "fail" || whenNotMatchedMode == "discard") {
insertData(outCollById);
}
// Actually execute the pipeline and make sure it works as expected.
assert.doesNotThrow(() => inColl.aggregate([{
$merge: {
into: outCollById.getName(),
whenMatched: whenMatchedMode,
whenNotMatched: whenNotMatchedMode
}
}]));
assert.eq(outCollById.find().itcount(), numDocs);
// Test the same thing but in a pipeline where the output collection's shard key differs
// from the input collection's.
explain = inColl.explain().aggregate([{
$merge: {
into: outCollBySK.getName(),
whenMatched: whenMatchedMode,
whenNotMatched: whenNotMatchedMode
}
}]);
assertMergeRunsOnShards(explain);
// Again, test that execution works as expected.
assert.eq(outCollBySK.find().itcount(), 0);
if (whenNotMatchedMode == "fail" || whenNotMatchedMode == "discard") {
insertData(outCollBySK);
}
assert.doesNotThrow(() => inColl.aggregate([{
$merge: {
into: outCollBySK.getName(),
whenMatched: whenMatchedMode,
whenNotMatched: whenNotMatchedMode
}
}]));
assert.eq(outCollBySK.find().itcount(), numDocs);
});
st.stop();
}());
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