I am looking to create a bulk spl-token airdrop script using nodeJS and Solana npm packages.
I know that we can add multiple instructions to a transaction but I suppose, each instruction would have a different size.
How to calculate how many (X type of) instructions can be added to a transaction?
I don't think there is a limit, but every transaction must stay below 1232 bytes. So you can calculate it when you know the size of your instructions. (1232 bytes - (signers, feepayer, account keys etc) / instruction size) should give you a good idea.
At a practical level, you’re limited by the total transaction size of roughly 1kb. Also, different instructions have different data dependencies so it’s impossible to give a concrete number.
I believe there is a internal instruction index that is set as a byte, so I think you’re limited to at most 256 instructions per transaction but you’ll have a hard time reaching that number due to the 1kb limit.
I recently solved this problem by creating 2 transactions. Let's call it tx 1 and 2.
If I added an instruction to tx 2 and serialize it successfully without an exception, I add it to tx 1.
I ran this over a loop, and found 55 instructions to be the limit for a transaction for my particular use case.
I then sign and transmit tx 1.
A Solana transaction may have one or more instructions that each list the inputs and addresses of an on-chain application. There is no stated restriction on the size of instruction, although it should be noted that a transaction's total serialized size cannot be greater than 1232 bytes.
