I am using connection pool in pg node js module.
As I understand when you are using connection pool, your connections created for you, and stored, when you need it, some method evoked, and you get already instantiated connection.
Now about pg:
Simple code
pg.connect(conString, function (err, client, done) {
if (err) {
callback(err);
} else {
client.query('SELECT * FROM users', function (err, result) {
done();
if (err) callback(err);
callback(null, result.rows);
});
}
});
When I call pg.connect method, I assume that, I get already instantiated connection from pool, when I call done I return my connection to the pool.
Now I want to debug my application, I can forgot to call done or do it not efficient way.
How can I print number of busy connections? Or another way to debug approach. Thank you in advance.
I had some problem, when request to my route hanging for 30 seconds, I suppose that it is, because I didn't return my connection to the pool.
From pg module documentation pages
var pg = require('pg');
pg.connect(function(err, client, done) {
var pool = pg.pools.getOrCreate();
console.log(pool.getPoolSize()); //1
console.log(pool.availableObjectsCount()); //0
done();
console.log(pool.getPoolSize()); //1
console.log(pool.availableObjectsCount()); //1
});
Hope this helps...
Related
What is the recommended way to establish database connection and close it properly in Node.js using tedious?
For each and every request we are creating new connection and processing the request then closing them in callback.
app.get('/getData/:id', function(req, res){
var id = req.params.id;
var sqlGet = "exec MyStoreProcedure #Id='" + id + "'";
var connection = new Connection(config);
var request = new Request(sqlGet, function(err, result){
connection.close();
if(err)
console.log(err);
else
res.send(result);
});
connection.on('connect', function(err) {
if (err)
{
console.log(err)
}else{
console.log("Connected");
connection.execSql(request);
}
});
});
Is there any other recommended approach to handle this scenario?
UPDATE (Oct 19, 2020):
It appears that tedious-connection-pool is no longer supported/outdated. I've migrated my code to mssql: https://www.npmjs.com/package/mssql
Previous Answer:
You should check out tedious-connection-pool: https://github.com/tediousjs/tedious-connection-pool.
This makes it easy to manage and reuse connections rather than open/close connections continuously.
As part of using connnection pooling, you should extract it out into a separate file so it can be reused across your application.
I have this database connection. Inside the function where the comment is located, there is a data update cycle for rest api. The data is updated, but when the data in the Oracle database is updated, the connection may fail and after that all subsequent updated data will get undefined. How can you properly connect to the database so that there are no failures?
oracledb.getConnection(
{
user: db.user,
password: db.password,
connectString: db.connectString
},
connExecute
);
function connExecute(err, connection) {
if (err) {
console.error(err.message);
return;
}
sql = `SELECT * FROM db.test`;
connection.execute(sql, {}, { outFormat: oracledb.OBJECT },
function (err, db) {
if (err) {
console.error(err.message);
connRelease(connection);
return;
}
// data update loop
connRelease(connection);
});
}
function connRelease(connection) {
connection.close(
function (err) {
if (err) {
console.error(err.message);
}
});
}
You should be using a connection pool. Connection pools have built-in logic to detect connections with issues and create new connections transparently. See this series on creating a REST API for more details: https://jsao.io/2018/03/creating-a-rest-api-with-node-js-and-oracle-database/
Keep in mind that issues can still happen, so you have to handle errors as needed for your application.
Mostly you add listener on connection object and on dissociation or failure again create connection. With minor changes you can adopt this approach and use listeners to check if connection is available if not connect again. There could be several reason that results in connection closing better handle exceptions, check if still connected and reconnect in case of error.
Or you can try this NPM this will do reconnection for you
https://www.npmjs.com/package/oracledb-autoreconnect
Ping me if you need calcification.
var dbConfig = {
host: '----',
user: '----',
password: '----',
database: '----',
port: ----
};
var connection;
function handleDisconnect() {
connection = <obj>.getConnection(dbConfig);
// Recreate the connection, since the old one cannot be reused.
connection.connect( function onConnect(err) {
// The server is either down
if (err) {
// or restarting (takes a while sometimes).
console.log('error when connecting to db:', err);
setTimeout(handleDisconnect, 10000);
// We introduce a delay before attempting to reconnect,
}
// to avoid a hot loop, and to allow our node script to
});
// process asynchronous requests in the meantime.
// If you're also serving http, display a 503 error.
connection.on('error', function onError(err) {
console.log('db error', err);
if (err.code == 'PROTOCOL_CONNECTION_LOST') {
handleDisconnect();
// lost due to either server restart, or a
} else {
// connnection idle timeout (the wait_timeout
throw err;
// server variable configures this)
}
});
}
handleDisconnect();
My stack is node, express and the pg module. I really try to understand by the documentation and some outdated tutorials. I dont know when and how to disconnect and to end a client.
For some routes I decided to use a pool. This is my code
const pool = new pg.Pool({
user: 'pooluser',host: 'localhost',database: 'mydb',password: 'pooluser',port: 5432});
pool.on('error', (err, client) => {
console.log('error ', err); process.exit(-1);
});
app.get('/', (req, res)=>{
pool.connect()
.then(client => {
return client.query('select ....')
.then(resolved => {
client.release();
console.log(resolved.rows);
})
.catch(e => {
client.release();
console.log('error', e);
})
pool.end();
})
});
In the routes of the CMS, I use client instead of pool that has different db privileges than the pool.
const client = new pg.Client({
user: 'clientuser',host: 'localhost',database: 'mydb',password: 'clientuser',port: 5432});
client.connect();
const signup = (user) => {
return new Promise((resolved, rejeted)=>{
getUser(user.email)
.then(getUserRes => {
if (!getUserRes) {
return resolved(false);
}
client.query('insert into user(username, password) values ($1,$2)',[user.username,user.password])
.then(queryRes => {
client.end();
resolved(true);
})
.catch(queryError => {
client.end();
rejeted('username already used');
});
})
.catch(getUserError => {
return rejeted('error');
});
})
};
const getUser = (username) => {
return new Promise((resolved, rejeted)=>{
client.query('select username from user WHERE username= $1',[username])
.then(res => {
client.end();
if (res.rows.length == 0) {
return resolved(true);
}
resolved(false);
})
.catch(e => {
client.end();
console.error('error ', e);
});
})
}
In this case if I get a username already used and try to re-post with another username, the query of the getUser never starts and the page hangs. If I remove the client.end(); from both functions, it will work.
I am confused, so please advice on how and when to disconnect and to completely end a pool or a client. Any hint or explanation or tutorial will be appreciated.
Thank you
First, from the pg documentation*:
const { Pool } = require('pg')
const pool = new Pool()
// the pool with emit an error on behalf of any idle clients
// it contains if a backend error or network partition happens
pool.on('error', (err, client) => {
console.error('Unexpected error on idle client', err) // your callback here
process.exit(-1)
})
// promise - checkout a client
pool.connect()
.then(client => {
return client.query('SELECT * FROM users WHERE id = $1', [1]) // your query string here
.then(res => {
client.release()
console.log(res.rows[0]) // your callback here
})
.catch(e => {
client.release()
console.log(err.stack) // your callback here
})
})
This code/construct is suficient/made to get your pool working, providing the your thing here things. If you shut down your application, the connection will hang normaly, since the pool is created well, exactly not to hang, even if it does provides a manual way of hanging,
see last section of the article.
Also look at the previous red section which says "You must always return the client..." to accept
the mandatory client.release() instruction
before accesing argument.
you scope/closure client within your callbacks.
Then, from the pg.client documentation*:
Plain text query with a promise
const { Client } = require('pg').Client
const client = new Client()
client.connect()
client.query('SELECT NOW()') // your query string here
.then(result => console.log(result)) // your callback here
.catch(e => console.error(e.stack)) // your callback here
.then(() => client.end())
seems to me the clearest syntax:
you end the client whatever the results.
you access the result before ending the client.
you don´t scope/closure the client within your callbacks
It is this sort of oposition between the two syntaxes that may be confusing at first sight, but there is no magic in there, it is implementation construction syntax.
Focus on your callbacks and queries, not on those constructs, just pick up the most elegant for your eyes and feed it with your code.
*I added the comments // your xxx here for clarity
You shouldn't disconnect the pool on every query, connection pool is supposed to be used to have "hot" connections.
I usually have a global connection on startup and the pool connection close on (if) application stop; you just have to release the connection from pool every time the query ends, as you already do, and use the same pool also in the signup function.
Sometimes I need to preserve connections, I use a wrapper to the query function that checks if the connection is active or not before perform the query, but it's just an optimization.
In case you don't want to manage open/close connections/pool or release, you could try https://github.com/vitaly-t/pg-promise, it manage all that stuff silently and it works well.
The documentation over node-postgres's github says:
pro tip: unless you need to run a transaction (which requires a single client for multiple queries) or you have some other edge case like streaming rows or using a cursor you should almost always just use pool.query. Its easy, it does the right thing ™️, and wont ever forget to return clients back to the pool after the query is done.
So for non-transactional query, calling below code is enough.
var pool = new Pool()
pool.query('select username from user WHERE username= $1',[username], function(err, res) {
console.log(res.rows[0].username)
})
By using pool.query, the library will take care of releasing the client after the query is done.
Its quite simple, a client-connection (single connection) opens up, query with it, once you are done you end it.
The pool concept is different, in the case of mysql : you have to .release() the connection back to the pool once you are done with it, but it seems that with pg is a different story:
From an issue on the github repo : Cannot use a pool after calling end on the pool #1635
"Cannot use a pool after calling end on the pool"
You can't reuse a pool after it has been closed (i.e. after calling
the .end() function). You would need to recreate the pool and discard
the old one.
The simplest way to deal with pooling in a Lambda is to not do it at
all. Have your database interactions create their own connections and
close them when they're done. You can't maintain a pool across
freeze/thaw cycles anyway as the underlying TCP sockets would be
closed.
If opening/closing the connections becomes a performance issue then
look into setting up an external pool like pgbouncer.
So I would say that your best option is to not end the pool, unless you are shutting down the server
I am using node-postgres in my application.
I would like to know the best practices that I want to follow to ensure the stable connection.
following is the code I'm using right now,
exports.getAll = function (args, callback) {
helper.client = new pg.Client('tcp://postgres:system6:5432#192.168.143.11/abc_dev');
helper.client.connect();
helper.client.query('select count(1) as total_records from facilities', function(err,response){
helper.client.query('select * ,'+response.rows[0].total_records+' as total_records from facilities',
function(err,response){
callback(response);
helper.client.end.bind(helper.client);
});
});
};
As you can see in the code I'm connecting the DB for every request and disconnect once the query has executed. I have one more idea where I can connect the DB globally only once and execute the query using the opened connection. The code look like
helper.client = new pg.Client('tcp://postgres:system6:5432#192.168.143.11/abc_dev');
helper.client.connect();
exports.getAll = function (args, callback) {
helper.client.query('select count(1) as total_records from facilities', function(err,response){
helper.client.query('select * ,'+response.rows[0].total_records+' as total_records from facilities',
function(err,response){
callback(response);
});
});
};
Here the connection never ends. As of my knowledge I am unable to decide which one is best.
Please suggest.
Thanks..
There is an example in the node-postgres wiki. It connects whenever a request is handled:
var server = http.createServer(function(req, res, next) {
pg.connect(function(err, client, done) {
This is what I think is right, too: Your connection should be in request scope.
I have been playing with Node.js for some time.
I have the following piece of script in my server:
socket.on('auth', function(uid, key) {
client.hgetall(uid, function (err, data) {
console.log(data);
if(key != data['key']) {
socket.disconnect();
}
this.user = data;
});
});
socket.on('loginGame', function(gameId) {
checkAuth();
console.log(user);
if(!games[gameId]) {
games[gameId] = {};
}
games[gameId][uid] = uid;
});
In my client;
socket.on('connect', function(){
socket.emit('auth', 1, 1);
socket.emit('loginGame', 1);
});
When I run this code, loginGame function finishes before auth function as I am doing I/O (using redis). I know this a feature of node.js, but I think I am missing something. How can I overcome this issue as auth function needs to finish before running any function. (I have a couple of more functions which need to run in serial)
I have found a node.js module: https://github.com/creationix/step . However, is this the only option? I think this is something most node.js developer might need. I am not that good at JS either.
What is the best and most elegant way of solving this issue?
Thanks,
Have the server send back an acknowledgement when auth is successful, and send loginGame in the handler for that message.