Hey guys... so I made my first purchase using poloniex (usually I just use shapeshift) and I just tried to withdraw while using the payment ID and everything. I've been waiting like 10 minutes now and I still haven't seen it in mymonero or on the block explorer, should I be worried?
I haven't used Polo in a while but as I remember it they send a confirmation email which you have to verify. I don't believe withdrawals are instant although I remember them being quick. No need to use a payment ID when sending to yourself, was the Payment ID generated by MyMonero?
Edit: the post I replied to was removed. I assume the Monero was received.
nioc is correct but I want to clarify the purpose of the payment id so you understand why some use it (like exchanges) while others do not. If two people owe you exactly 100xmr and both claim they paid you but you only received one transaction for 100xmr how do you know which person paid you?
Asking someone to include a payment ID (like an exchange requests for deposits) allows you to easily connect the payment with the person you provided that payment ID.
When you are sending xmr to yourself from an exchange you know where the xmr came from and probably don't need a payment ID.
I guess I'm a little slow when learning these things, but wouldn't you always want to include a payment ID when conducting business with someone in that case? Even in regards to sending a payment to yourself from an exchange... if you don't include the payment ID when transacting XMR to your wallet, regardless of where it's coming from, wouldn't you always want to include it so you can be able to see it on the blockchain just for reassurance purposes? Is there an advantage for leaving out the payment ID in some cases? Etc.
If you need reassurance, then yes.
However, in the whole process there's also a transaction ID. Basically, its an identifier for the whole transaction, and this transaction ID is public. So, if you were to send some monero to someone, your wallet software would say "yay you've sent money. Your transaction ID is (somestringofnumbers). So, if you go and paste this transaction ID on the blockchain, you can find your transaction. Of course, the transaction information is all cryptographically garbled nonsense thanks to ring signatures + stealth addresses.
The primary reason now for leaving out a payment ID is that its not encrypted / hidden / etc - its all public information (bitcoin style - whatever you push to the blockchain is whats recorded on the blockchain in more or less plain text... well, plain hex). So, this could create the same kind of information leak that can occur in bitcoin. Say, for instance, you constantly use a payment ID of s230909hfkhsdfs. Lets say you use this payment ID for years, for whatever reason. If it was ever leaked that this was your payment ID, then boom - now anyone can look at the blockchain and find which transactions are yours, ala bitcoin style. All of the ring signatures and stealth addressing is wasted.
It has been pointed out that the sloppy nature of payment IDs hints that these were tacked on in the final stages of cryptonote development when the original developers realized that their system was so good that it would be impossible to identify that a particular incoming transaction was from bob, if bob is sending money to a store or an exchange.