Using the mongodb node driver version 3.6.10, I've set the poolSize and maxPoolSize to be 6 (not 100% sure which option is the correct one for this version, but both are set).
However, in certain situations - I see client.topology.s.sessionPool.sessions.length of 9.
Have I incorrectly configured the connection? If not, in which circumstances would the mongo driver go over the maxPoolSize?
poolSize is related to a connectionPool where a sessionPool is fully unrelated and different stuff
Related
The default value for maxPoolSize on the MongoClient is 100.
How would one know if the default value, 100, is the optimal value? Is there a formula, a way of calculating to determine the ideal maxPoolSize?
Thanks a lot.
The pool size is solely dependent on the driver you are using, for Node.js minimum is 5 which is default and the maximum is 100(default).
Pool size helps to make the concurrent requests to the DB and it depends upon how much concurrent connection(queries you can run on) you need to create from the application. You can increase it based on your usage- that you have to need more than 100 connections at a time with DB or you need some connections for long-running tasks etc.
And these connections are of course based on the server that you are running the DB on. Mongo atlas does provide certain clusters that can have up to 1500 connections at a time.
You should check this post to see how does it impact application performance.
I have a serious problem in production causing the application to become unresponsive and output the following error:
Knex: Timeout acquiring a connection. The pool is probably full. Are you missing a .transacting(trx) call?
A running hypothesis is some operations are holding onto long-running Knex transactions. Enough of them to reach the pool size, basically.
Is there a way to query the KnexJS API for how many pool connections are in use at any one time? Unfortunately since KnexJS occupies the max pool settings from the config, it can be hard to know how many are actually in use. From the postgres end, it seems like KnexJS is idling on all of its connections when they are not in use.
Is there a good way to instrument Knex transaction and transacting with some kind of middleware or hook? Another useful thing is to log the callstack of any transaction (or any longer than, say, 7 seconds). One challenge is I have calls to Knex transaction and transacting throughout my project. Maybe it's a long shot.
Any advice is greatly appreciated.
System Information
KnexJS version: 0.12.6 (we will update in the next month)
Database + version: Postgres 9.6
OS: Heroku Linux (Ubuntu?)
Easiest was to see whats happening on connection pool level is to run knex with DEBUG=knex:* environment variable set, which will print quite a lot debug info whats happening inside knex. Those logs shows for example when connections are fetched from pool and returned to there and every ran query too.
There are couple of global events that you can use to hookup to every query, but there is not any for hooking to transactions. Here is related question where I have written some example code how to actually measure transaction durations with query hooks though: Tracking DB querying time - Bookshelf/knex It probably leaks some memory, so its not very production ready solution, but for your debugging purposes it might be helpful.
I'm using Node js and Postgresql and trying to be most efficient in the connections implementation.
I saw that pg-promise is built on top of node-postgres and node-postgres uses pg-pool to manage pooling.
I also read that "more than 100 clients at a time is a very bad thing" (node-postgres).
I'm using pg-promise and wanted to know:
what is the recommended poolSize for a very big load of data.
what happens if poolSize = 100 and the application gets 101 request simultaneously (or even more)?
Does Postgres handles the order and makes the 101 request wait until it can run it?
I'm the author of pg-promise.
I'm using Node js and Postgresql and trying to be most efficient in the connections implementation.
There are several levels of optimization for database communications. The most important of them is to minimize the number of queries per HTTP request, because IO is expensive, so is the connection pool.
If you have to execute more than one query per HTTP request, always use tasks, via method task.
If your task requires a transaction, execute it as a transaction, via method tx.
If you need to do multiple inserts or updates, always use multi-row operations. See Multi-row insert with pg-promise and PostgreSQL multi-row updates in Node.js.
I saw that pg-promise is built on top of node-postgres and node-postgres uses pg-pool to manage pooling.
node-postgres started using pg-pool from version 6.x, while pg-promise remains on version 5.x which uses the internal connection pool implementation. Here's the reason why.
I also read that "more than 100 clients at a time is a very bad thing"
My long practice in this area suggests: If you cannot fit your service into a pool of 20 connections, you will not be saved by going for more connections, you will need to fix your implementation instead. Also, by going over 20 you start putting additional strain on the CPU, and that translates into further slow-down.
what is the recommended poolSize for a very big load of data.
The size of the data got nothing to do with the size of the pool. You typically use just one connection for a single download or upload, no matter how large. Unless your implementation is wrong and you end up using more than one connection, then you need to fix it, if you want your app to be scalable.
what happens if poolSize = 100 and the application gets 101 request simultaneously
It will wait for the next available connection.
See also:
Chaining Queries
Performance Boost
what happens if poolSize = 100 and the application gets 101 request simultaneously (or even more)? Does Postgres handles the order and makes the 101 request wait until it can run it?
Right, the request will be queued. But it's not handled by Postgres itself, but by your app (pg-pool). So whenever you run out of free connections, the app will wait for a connection to release, and then the next pending request will be performed. That's what pools are for.
what is the recommended poolSize for a very big load of data.
It really depends on many factors, and no one will really tell you the exact number. Why not test your app under huge load and see in practise how it performs, and find the bottlenecks.
Also I find the node-postgres documentation quite confusing and misleading on the matter:
Once you get >100 simultaneous requests your web server will attempt to open 100 connections to the PostgreSQL backend and 💥 you'll run out of memory on the PostgreSQL server, your database will become unresponsive, your app will seem to hang, and everything will break. Boooo!
https://github.com/brianc/node-postgres
It's not quite true. If you reach the connection limit at Postgres side, you simply won't be able to establish a new connection until any previous connection is closed. Nothing will break, if you handle this situation in your node app.
I have NodeJS API using mongoose to talk to Mongo DB. Initially, I had the default connection pool size of 5 and later increased it to 20 during performance testing. However, it's bothering me if there is a way to log the actual number of DB instances being used. It could be 10 or 15. But there is no way to figure it out. Has anyone tried to solve this?
I also came across an article that said that NodeJS uses threads internally (max 4) that would restrict the actual DB threads. Will update this question with the link later.
I am building a simple application using Node.js and MongoDB through the MongoJS driver. I am aiming at some heavy load (round 10000 users in 10 mins with sessions of approx 30s)
I am using connection pooling, and by default mongojs creates 5 connections which are expected to be shared. I would like to enlarge this value to increase efficiency, otherwise a bunch of requests will be waiting for a connection which is highly undesirable.
I have found this which explains how to increase the pool size if using the native driver
http://technosophos.com/content/nodejs-connection-pools-and-mongodb
I know that mongojs is a wrapper for the native driver, but is there a way to set the connection pool size in mongojs? or is it something you have to do from the driver.. but if so how can you use the driver and mongojs at the same time? Can anyone point me in the right direction?
Thanks so much.
Pool size options can be specified as part of the connection string. The options are listed in the MongoDB documentation. Connection string parameters are mentioned in the MongoJS documentation but it's not particularly obvious that one would find the answer there.
var db = mongojs('mongodb://localhost/mydb?maxPoolSize=200');
A minPoolSize can also be specified, however this option is not supported by all drivers. I am pretty sure that the native js driver does not support this option. From memory the native js driver keeps a minimum pool of 5 connections.
The default maxPoolSize value is 100.