How to increase transaction file size?

[wsxdrfv]

I found that when try to send big number like 300,000 coin at once, then daemon become slow, then error says transaction size limit is over.

So I think this because, wallet try to gather many address's balance to make total 300,000, so when it become exceed size, then it errors, right?

So how can I increase this size at sourcecode?

[mocacinno]

I found that when try to send big number like 300,000 coin at once, then daemon become slow, then error says transaction size limit is over.

So I think this because, wallet try to gather many address's balance to make total 300,000, so when it become exceed size, then it errors, right?

So how can I increase this size at sourcecode?

Which wallet are you using? I vaguely remember bitcoin core used to have a 100 kb limit, but afaik it has been removed a long time ago.
Offcourse, with a non-segwit wallet, the maximum transaction size is 1Mb, with a segwit wallet the size of the transaction without the witness data is 1Mb.

BTW: it doesn't matter how much BTC you're trying to spend. It matters how many unspent outputs you're using as an input to create the transactions, and how many addresses you're funding (how many new unspent outputs will be created by the new transaction).

If you use 100 unspent outputs with a value of 0.001 BTC as an input for a transaction with 1 output, the transaction will have about the same size as when you're using 100 unspent outputs with a value of 1 BTC as an input and 1 output (eventough the maximum output value of the first transaction would be <0.1BTC while the value of the second one would be < 100 BTC).

A workaround for your problem would probably be to combine unspent outputs first.
For example, you have 1000 unspent outputs and need them to fund 1ReceivingAddress.
If the transaction using the 1000 unspent outputs as an input is to large, you can create 5 new addresses and fund them using 200 of your unspent outputs. Once those 5 transactions are confirmed, your wallet now holds 5 unspent outputs instead of 1000, so the transaction funding 1ReceivingAddress will use 5 unspent outputs as an input and will be relatively small.

[DannyHamilton]

I found that when try to send big number like 300,000 coin at once, then daemon become slow, then error says transaction size limit is over.

Somehow I doubt that you have access to 300,000 BTC that you can try to send.

If this is an altcoin question, then you'll need to move this thread to the altcoin sub-forum.  Altcions do lots of dumb things when they alter the code and they often break stuff.