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// Tests for the mongos explain command.
(function() {
'use strict';
// Create a cluster with 3 shards.
var st = new ShardingTest({shards: 2});
var db = st.s.getDB("test");
var explain;
// Setup a collection that will be sharded. The shard key will be 'a'. There's also an index on
// 'b'.
var collSharded = db.getCollection("mongos_explain_cmd");
collSharded.drop();
collSharded.ensureIndex({a: 1});
collSharded.ensureIndex({b: 1});
// Enable sharding.
assert.commandWorked(db.adminCommand({enableSharding: db.getName()}));
st.ensurePrimaryShard(db.getName(), st.shard1.shardName);
db.adminCommand({shardCollection: collSharded.getFullName(), key: {a: 1}});
// Pre-split the collection to ensure that both shards have chunks. Explicitly
// move chunks since the balancer is disabled.
assert.commandWorked(db.adminCommand({split: collSharded.getFullName(), middle: {a: 1}}));
printjson(db.adminCommand(
{moveChunk: collSharded.getFullName(), find: {a: 1}, to: st.shard0.shardName}));
assert.commandWorked(db.adminCommand({split: collSharded.getFullName(), middle: {a: 2}}));
printjson(db.adminCommand(
{moveChunk: collSharded.getFullName(), find: {a: 2}, to: st.shard1.shardName}));
// Put data on each shard.
for (var i = 0; i < 3; i++) {
collSharded.insert({_id: i, a: i, b: 1});
}
st.printShardingStatus();
// Test a scatter-gather count command.
assert.eq(3, collSharded.count({b: 1}));
// Explain the scatter-gather count.
explain = db.runCommand(
{explain: {count: collSharded.getName(), query: {b: 1}}, verbosity: "allPlansExecution"});
// Validate some basic properties of the result.
printjson(explain);
assert.commandWorked(explain);
assert("queryPlanner" in explain);
assert("executionStats" in explain);
assert.eq(2, explain.queryPlanner.winningPlan.shards.length);
assert.eq(2, explain.executionStats.executionStages.shards.length);
assert("serverInfo" in explain, explain);
assert.hasFields(explain.serverInfo, ['host', 'port', 'version', 'gitVersion']);
// An explain of a command that doesn't exist should fail gracefully.
explain = db.runCommand({
explain: {nonexistent: collSharded.getName(), query: {b: 1}},
verbosity: "allPlansExecution"
});
printjson(explain);
assert.commandFailed(explain);
// -------
// Setup a collection that is not sharded.
var collUnsharded = db.getCollection("mongos_explain_cmd_unsharded");
collUnsharded.drop();
collUnsharded.ensureIndex({a: 1});
collUnsharded.ensureIndex({b: 1});
for (var i = 0; i < 3; i++) {
collUnsharded.insert({_id: i, a: i, b: 1});
}
assert.eq(3, collUnsharded.count({b: 1}));
explain = db.runCommand({
explain: {
group: {
ns: collUnsharded.getName(),
key: "a",
cond: "b",
$reduce: function(curr, result) {},
initial: {}
}
},
verbosity: "allPlansExecution"
});
// Basic validation: a group command can only be passed through to an unsharded collection,
// so we should confirm that the mongos stage is always SINGLE_SHARD.
printjson(explain);
assert.commandWorked(explain);
assert("queryPlanner" in explain);
assert("executionStats" in explain);
assert.eq("SINGLE_SHARD", explain.queryPlanner.winningPlan.stage);
// The same group should fail over the sharded collection, because group is only supported
// if it is passed through to an unsharded collection.
explain = db.runCommand({
explain: {
group: {
ns: collSharded.getName(),
key: "a",
cond: "b",
$reduce: function(curr, result) {},
initial: {}
}
},
verbosity: "allPlansExecution"
});
printjson(explain);
assert.commandFailed(explain);
// -------
// Explain a delete operation and verify that it hits all shards without the shard key
explain = db.runCommand({
explain: {delete: collSharded.getName(), deletes: [{q: {b: 1}, limit: 0}]},
verbosity: "allPlansExecution"
});
assert.commandWorked(explain, tojson(explain));
assert.eq(explain.queryPlanner.winningPlan.stage, "SHARD_WRITE");
assert.eq(explain.queryPlanner.winningPlan.shards.length, 2);
assert.eq(explain.queryPlanner.winningPlan.shards[0].winningPlan.stage, "DELETE");
assert.eq(explain.queryPlanner.winningPlan.shards[1].winningPlan.stage, "DELETE");
// Check that the deletes didn't actually happen.
assert.eq(3, collSharded.count({b: 1}));
// Explain a delete operation and verify that it hits only one shard with the shard key
explain = db.runCommand({
explain: {delete: collSharded.getName(), deletes: [{q: {a: 1}, limit: 0}]},
verbosity: "allPlansExecution"
});
assert.commandWorked(explain, tojson(explain));
assert.eq(explain.queryPlanner.winningPlan.shards.length, 1);
// Check that the deletes didn't actually happen.
assert.eq(3, collSharded.count({b: 1}));
// Check that we fail gracefully if we try to do an explain of a write batch that has more
// than one operation in it.
explain = db.runCommand({
explain: {
delete: collSharded.getName(),
deletes: [{q: {a: 1}, limit: 1}, {q: {a: 2}, limit: 1}]
},
verbosity: "allPlansExecution"
});
assert.commandFailed(explain, tojson(explain));
// Explain a multi upsert operation and verify that it hits all shards
explain = db.runCommand({
explain:
{update: collSharded.getName(), updates: [{q: {}, u: {$set: {b: 10}}, multi: true}]},
verbosity: "allPlansExecution"
});
assert.commandWorked(explain, tojson(explain));
assert.eq(explain.queryPlanner.winningPlan.shards.length, 2);
assert.eq(explain.queryPlanner.winningPlan.stage, "SHARD_WRITE");
assert.eq(explain.queryPlanner.winningPlan.shards.length, 2);
assert.eq(explain.queryPlanner.winningPlan.shards[0].winningPlan.stage, "UPDATE");
assert.eq(explain.queryPlanner.winningPlan.shards[1].winningPlan.stage, "UPDATE");
// Check that the update didn't actually happen.
assert.eq(0, collSharded.count({b: 10}));
// Explain an upsert operation and verify that it hits only a single shard
explain = db.runCommand({
explain: {update: collSharded.getName(), updates: [{q: {a: 10}, u: {a: 10}, upsert: true}]},
verbosity: "allPlansExecution"
});
assert.commandWorked(explain, tojson(explain));
assert.eq(explain.queryPlanner.winningPlan.shards.length, 1);
// Check that the upsert didn't actually happen.
assert.eq(0, collSharded.count({a: 10}));
// Explain an upsert operation which cannot be targeted, ensure an error is thrown
explain = db.runCommand({
explain: {update: collSharded.getName(), updates: [{q: {b: 10}, u: {b: 10}, upsert: true}]},
verbosity: "allPlansExecution"
});
assert.commandFailed(explain, tojson(explain));
st.stop();
})();
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