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added replication support #267

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icodeforlove
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Tests still need to be made, but heres a basic proof of concept of how we would handle multiple connection pools.

var sequel = new Sequel(schema, sqlOptions);

// Build a query for the specific query strategy
try {
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this seems odd, I may have squished someone elses commit here.

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Try pulling in the latest from master

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Bump? :)

@RWOverdijk
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Does this change the connection name dynamically, too? I mean, the logs are useful if they also log which server from the pools you're connecting to?

@RWOverdijk
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I wouldn't call this replication. I'm thinking balanced?

I like the initiative on this PR, 👍 for that.

@@ -1117,8 +1106,9 @@ module.exports = (function() {
* @param {Function} fn
* @param {[type]} cb
*/
function spawnConnection(connectionName, fn, cb) {
function spawnConnection(queryType, connectionName, fn, cb) {

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Should be careful that this doesn't break anywhere. Did you check for all uses? Does this get exposed to user code? (if so, it's a BC break).

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Looked like an internal call, but someone else may be more aware of the ramifications.

@icodeforlove
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@RWOverdijk this naming convention was taken from sequelize

http://docs.sequelizejs.com/en/1.7.0/docs/usage/#read-replication

as for logs yes it logs which index and which pool its from

@RWOverdijk
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Ah okay that makes sense. Still though, replication...? :p

@icodeforlove
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I mean it makes sense to me from a DBA perspective because thats how the servers are actually configured for replication.

@devinivy
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Exciting stuff!

@particlebanana
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@icodeforlove @RWOverdijk @devinivy this is interesting. From a glance this actually looks like something we can support on pretty much all adapters by creating multiple connection pools. Although in the sequelize docs it says: Note: Read replication only works for MySQL at the moment! is this a limitation of the actual databases?

Not being a DBA how does this work with transactions? Does it start a transaction on both the read connection and the write connection?

@devinivy
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Read replication is a feature of certain types of databases. The databases coordinate with each other to keep multiple read replicas in sync with some master database. Transactions should be supported– I believe they occur on the master database, then the replicas lag slightly behind, catching-up on all the transactions that have occurred on master.

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