I am just starting to use ReactiveMongo with Play 2 (scala).
Should I store a singleton object with the connection details and a return of the database (connection.get.db("mydb")) or keep the connection alive indefinitely.
I am used to JDBC connection pools so am unsure what the performant way to use ReactiveMongo and Mongo is.
Sorry if this is not very well formed question, I am fumbling in the dark a bit.
Thanks
From this documentation
http://reactivemongo.org/releases/0.10/api/index.html#reactivemongo.api.MongoDriver
there is optional parameter
nbChannelsPerNode Number of channels to open per node. Defaults to 10.
This looks like that the returned object (MongoConnection) is connection pool itself. So you should use it as singleton and not create a new instances for each request.
Related
I have documents in different MongoDB databases referencing each other (mongoengine's LazyRefereneceField), so each time I need to get the field's value, I need to connect and disconnect from the field's relevant database, which I find very inefficient.
I've read about connection pooling, but I can't find a solution on how to implement it using MongoEngine. How can I create a connection pool and reuse connections from it every time I need to the value for a LazyReferenceField?
MongoEngine is managing the connection globally (i.e once connected, it auto-magically re-use that connection), usually you call connect just once, when the application/script starts and then you are good to go, and don't need to interfere with the connection.
LazyReferenceField is not different from any other field (ReferenceField, StringField, etc) in that context. The only difference is that it's not doing the de-referencing immediatly but only when you explicitly request it with the .fetch method
In order to improve application performance, thought of trying & creating the redis connection pool to share the load, instead of rotating single same redis connection to cater all the incoming requests, as the per the suggestion by Redis team here
What would be the best way of creating StackExchange.Redis connection pool for same Redis server config using C# & keep rotating one connection after another from the pool to cater the incoming request?
Is there any SDK/nuget package available to create Redis connection pool?
At present we are reuse the single ConnectionMultiplexer created using Lazy pattern via singleton class which will initiate single redis connection object on the very first request & will be reused throughout the application lifetime.
P.S: thread safe can be ignored as all the instance in the connection pool using same Redis server config.
There's a library that I have implemented two years ago exactly for that requirement. It's thread safe and it creates the connection pool lazily.
Also, you can use built in implementations of connection selection strategy such as round-robin and load based.
The NuGet is https://www.nuget.org/packages/StackExchange.Redis.MultiplexerPool/
You can see sample here https://github.com/mataness/StackExchange.Redis.MultiplexerPool/blob/master/samples/RedisConnectionPoolConsoleApp/Program.cs
I have a Node.js script and a PostgreSQL database, and I'll be using a library that maintains a pool of connections to the database.
Say I have a script that queries the database multiple times (not a transaction) at different parts of the script, how do I tell if I should acquire a single connection/client and reuse it throughout*, or acquire a new client from the pool for each query? (Both works but which has better performance?)
*task in the pg-promise library, connect in the node-postgres library.
...
// Acquire connection from pool.
(Database query)
(Non-database-related code)
(Database query)
// Release connection to pool.
...
or
...
// Acquire connection from pool.
(Database query)
// Release connection to pool.
(Non-database-related code)
// Acquire connection from pool.
(Database query)
// Release connection to pool.
...
I am not sure, how the pool you are using works, but normally they should reuse the connections (don't disconnect after use), so you do not need to be concerned with caching connections.
You can use node-postgres module that will make you task easier.
And about your question when to use pool here is the brief answer.
PostgreSQL server can only handle 1 query at a time per connection.
That means if you have 1 global new pg.Client() connected to your
backend your entire app is bottleknecked based on how fast postgres
can respond to queries. It literally will line everything up, queuing
each query. Yeah, it's async and so that's alright...but wouldn't you
rather multiply your throughput by 10x? Use pg.connect set the
pg.defaults.poolSize to something sane (we do 25-100, not sure the
right number yet).
new pg.Client is for when you know what you're doing. When you need a
single long lived client for some reason or need to very carefully
control the life-cycle. A good example of this is when using
LISTEN/NOTIFY. The listening client needs to be around and connected
and not shared so it can properly handle NOTIFY messages. Other
example would be when opening up a 1-off client to kill some hung
stuff or in command line scripts.
here is the link of that module.
Hopefully this will help.
https://github.com/brianc/node-postgres
You can see the documentation over there and about the pooling. Thanks :)
And about closing the pool it provides the callback done which can be called when you want to close that pool.
I'm using the Node native client 1.4 in my application and I found something in the document a little bit confusing:
A Connection Pool is a cache of database connections maintained by the driver so that connections can be re-used when new connections to the database are required. To reduce the number of connection pools created by your application, we recommend calling MongoClient.connect once and reusing the database variable returned by the callback:
Several questions come in mind when reading this:
Does it mean the db object also maintains the fail over feature provided by replica set? Which I thought should be the work of MongoClient (not sure about this but the C# driver document does say MongoClient maintains replica set stuff)
If I'm reusing the db object, when should I invoke the db.close() function? I saw the db.close() in every example. But shouldn't we keep it open if we want to reuse it?
EDIT:
As it's a topic about reusing, I'd also want to know how we can share the db in different functions/objects?
As the project grows bigger, I don't want to nest all the functions/objects in one big closure, but I also don't want to pass it to all the functions/objects.
What's a more elegant way to share it among the application?
The concept of "connection pooling" for database connections has been around for some time. It really is a common sense approach as when you consider it, establishing a connection to a database every time you wish to issue a query is very costly and you don't want to be doing that with the additional overhead involved.
So the general principle is there that you have an object handle ( db reference in this case ) that essentially goes and checks for which "pooled" connection it can use, and possibly if the current "pool" is fully utilized then and create another ( or a few others ) connection up to the pool limit in order to service the request.
The MongoClient class itself is just a constructor or "factory" type class whose purpose is to establish the connections and indeed the connection pool and return a handle to the database for later usage. So it is actually the connections created here that are managed for things such as replica set fail-over or possibly choosing another router instance from the available instances and generally handling the connections.
As such, the general practice in "long lived" applications is that "handle" is either globally available or able to be retrieved from an instance manager to give access to the available connections. This avoids the need to "establish" a new connection elsewhere in your code, which has already been stated as a costly operation.
You mention the "example" code which is often present through many such driver implementation manuals often or always calling db.close. But these are just examples and not intended as long running applications, and as such those examples tend to be "cycle complete" in that they show all of the "initialization", the "usage" of various methods, and finally the "cleanup" as the application exits.
Good application or ODM type implementations will typically have a way to setup connections, share the pool and then gracefully cleanup when the application finally exits. You might write your code just like "manual page" examples for small scripts, but for a larger long running application you are probably going to implement code to "clean up" your connections as your actual application exits.
It seems like the classical way to handle transactions with JDBC is to set auto-commit to false. This creates a new transaction, and each call to commit marks the beginning the next transactions.
On multithreading app, I understand that it is common practice to open a new connection for each thread.
I am writing a RMI based multi-client server application, so that basically my server is seamlessly spawning one thread for each new connection.
To handle transactions correctly should I go and create a new connection for each of those thread ?
Isn't the cost of such an architecture prohibitive?
Yes, in general you need to create a new connection for each thread. You don't have control over how the operating system timeslices execution of threads (notwithstanding defining your own critical sections), so you could inadvertently have multiple threads trying to send data down that one pipe.
Note the same applies to any network communications. If you had two threads trying to share one socket with an HTTP connection, for instance.
Thread 1 makes a request
Thread 2 makes a request
Thread 1 reads bytes from the socket, unwittingly reading the response from thread 2's request
If you wrapped all your transactions in critical sections, and therefore lock out any other threads for an entire begin/commit cycle, then you might be able to share a database connection between threads. But I wouldn't do that even then, unless you really have innate knowledge of the JDBC protocol.
If most of your threads have infrequent need for database connections (or no need at all), you might be able to designate one thread to do your database work, and have other threads queue their requests to that one thread. That would reduce the overhead of so many connections. But you'll have to figure out how to manage connections per thread in your environment (or ask another specific question about that on StackOverflow).
update: To answer your question in the comment, most database brands don't support multiple concurrent transactions on a single connection (InterBase/Firebird is the only exception I know of).
It'd be nice to have a separate transaction object, and to be able to start and commit multiple transactions per connection. But vendors simply don't support it.
Likewise, standard vendor-independent APIs like JDBC and ODBC make the same assumption, that transaction state is merely a property of the connection object.
It's uncommon practice to open a new connection for each thread.
Usually you use a connection pool like c3po library.
If you are in an application server, or using Hibernate for example, look at the documentation and you will find how to configure the connection pool.
The same connection object can be used to create multiple statement objects and these statement objects can then used by different threads concurrently. Most modern DBs interfaced by JDBC can do that. The JDBC is thus able to make use of concurrent cursors as follows. PostgreSQL is no exception here, see for example:
http://doc.postgresintl.com/jdbc/ch10.html
This allows connection pooling where the connection are only used for a short time, namely to created the statement object and but after that returned to the pool. This short time pooling is only recommended when the JDBC connection does also parallelization of statement operations, otherwise normal connection pooling might show better results. Anyhow the thread can continue work with the statement object and close it later, but not the connection.
1. Thread 1 opens statement
3. Thread 2 opens statement
4. Thread 1 does something Thread 2 does something
5. ... ...
6. Thread 1 closes statement ...
7. Thread 2 closes statement
The above only works in auto commit mode. If transactions are needed there is still no need to tie the transaction to a thread. You can just partition the pooling along the transactions that is all and use the same approach as above. But this is only needed not because of some socket connection limitation but because the JDBC then equates the session ID with the transaction ID.
If I remember well there should be APIs and products around with a less simplistic design, where teh session ID and the transaction ID are not equated. In this APIs you could write your server with one single database connection object, even when it does
transactions. Will need to check and tell you later what this APIs and products are.