mongodb/jstests/sharding/balance_repl.js

/**
 * Testing migrations are successful and immediately visible on the secondaries, when
 * secondaryThrottle is used.
 */
import {ShardingTest} from "jstests/libs/shardingtest.js";

// The mongod secondaries are set to priority 0 to prevent the primaries from stepping down during
// migrations on slow evergreen builders.
var s = new ShardingTest({
    shards: 2,
    other: {
        chunkSize: 1,
        rs0: {
            nodes: [
                {rsConfig: {}},
                {rsConfig: {priority: 0}},
            ],
        },
        rs1: {
            nodes: [
                {rsConfig: {}},
                {rsConfig: {priority: 0}},
            ],
        }
    }
});

assert.commandWorked(
    s.s0.adminCommand({enablesharding: 'TestDB', primaryShard: s.shard0.shardName}));

var bulk = s.s0.getDB('TestDB').TestColl.initializeUnorderedBulkOp();
for (var i = 0; i < 2100; i++) {
    bulk.insert({_id: i, x: i});
}
assert.commandWorked(bulk.execute({w: "majority"}));

assert.commandWorked(s.s0.adminCommand({shardcollection: 'TestDB.TestColl', key: {_id: 1}}));

for (i = 0; i < 20; i++) {
    assert.commandWorked(s.s0.adminCommand({split: 'TestDB.TestColl', middle: {_id: i * 100}}));
}

var collPrimary = (new Mongo(s.s0.host)).getDB('TestDB').TestColl;
assert.eq(2100, collPrimary.find().itcount());

var collSecondaryOk = (new Mongo(s.s0.host)).getDB('TestDB').TestColl;
collSecondaryOk.setSecondaryOk();
assert.eq(2100, collSecondaryOk.find().itcount());

assert.commandWorked(s.s0.adminCommand({
    moveChunk: 'TestDB.TestColl',
    find: {_id: 0},
    to: s.shard1.shardName,
    _secondaryThrottle: true,
    writeConcern: {w: 2},
    _waitForDelete: true
}));

assert.eq(2100,
          collSecondaryOk.find().itcount(),
          'Incorrect count when reading from secondary. Count from primary is ' +
              collPrimary.find().itcount());

s.stop();