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Separate oplog tail queries from other operations.

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This prevents the "look up last oplog entry" queries from taking several
seconds 1/5 of the time when the query is on the same pooled connection
as the awaitdata tail query.
This commit is contained in:
David Glasser
2013-10-16 14:12:07 -07:00
parent aae9fc23db
commit 599a2f928e
1 changed files with 18 additions and 6 deletions
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24
packages/mongo-livedata/mongo_driver.js
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@@ -229,8 +229,9 @@ var quotemeta = function (str) {
MongoConnection.prototype._startOplogTailing = function (oplogUrl, dbName) {
var self = this;
var oplogQueryConnection = null;
var oplogTailConnection = null;
var stopped = false;
var oplogConnection = null;
var tailHandle = null;
var readyFuture = new Future();
var nextId = 0;
@@ -292,7 +293,7 @@ MongoConnection.prototype._startOplogTailing = function (oplogUrl, dbName) {
// We need to make the selector at least as restrictive as the actual
// tailing selector (ie, we need to specify the DB name) or else we
// might find a TS that won't show up in the actual tail stream.
var lastEntry = oplogConnection.findOne(
var lastEntry = oplogQueryConnection.findOne(
OPLOG_COLLECTION, baseOplogSelector, {sort: {$natural: -1}});
if (!lastEntry) {
// Really, nothing in the oplog? Well, we've processed everything.
@@ -320,12 +321,23 @@ MongoConnection.prototype._startOplogTailing = function (oplogUrl, dbName) {
}
};
// Actually setting up the connection and tail blocks, so we do it "later".
// Setting up the connections and tail handler is a blocking operation, so we
// do it "later".
Meteor.defer(function () {
oplogConnection = new MongoConnection(oplogUrl);
// We make two separate connections to Mongo. The Node Mongo driver
// implements a naive round-robin connection pool: each "connection" is a
// pool of several (5 by default) TCP connections, and each request is
// rotated through the pools. Tailable cursor queries block on the server
// until there is some data to return (or until a few seconds have
// passed). So if the connection pool used for tailing cursors is the same
// pool used for other queries, the other queries will be delayed by seconds
// 1/5 of the time.
// XXX set the pool size for oplogTailConnection to 1
oplogTailConnection = new MongoConnection(oplogUrl);
oplogQueryConnection = new MongoConnection(oplogUrl);
// Find the last oplog entry. Blocks until the connection is ready.
var lastOplogEntry = oplogConnection.findOne(
var lastOplogEntry = oplogQueryConnection.findOne(
OPLOG_COLLECTION, {}, {sort: {$natural: -1}});
var oplogSelector = _.clone(baseOplogSelector);
@@ -341,7 +353,7 @@ MongoConnection.prototype._startOplogTailing = function (oplogUrl, dbName) {
var cursorDescription = new CursorDescription(
OPLOG_COLLECTION, oplogSelector, {tailable: true});
tailHandle = oplogConnection.tail(cursorDescription, function (doc) {
tailHandle = oplogTailConnection.tail(cursorDescription, function (doc) {
if (!(doc.ns && doc.ns.length > dbName.length + 1 &&
doc.ns.substr(0, dbName.length + 1) === (dbName + '.')))
throw new Error("Unexpected ns");