From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 2486FBC3 for ; Tue, 8 Dec 2015 04:58:10 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from azure.erisian.com.au (cerulean.erisian.com.au [106.187.51.212]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id B4109DF for ; Tue, 8 Dec 2015 04:58:09 +0000 (UTC) Received: from aj@azure.erisian.com.au (helo=sapphire.erisian.com.au) by azure.erisian.com.au with esmtpsa (Exim 4.84 #2 (Debian)) id 1a6ALm-0000vF-S2 for ; Tue, 08 Dec 2015 14:58:08 +1000 Received: by sapphire.erisian.com.au (sSMTP sendmail emulation); Tue, 08 Dec 2015 14:58:03 +1000 Date: Tue, 8 Dec 2015 14:58:03 +1000 From: Anthony Towns To: bitcoin-dev@lists.linuxfoundation.org Message-ID: <20151208045803.GA1042@sapphire.erisian.com.au> References: <20151208024224.GA32631@sapphire.erisian.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151208024224.GA32631@sapphire.erisian.com.au> User-Agent: Mutt/1.5.24 (2015-08-30) X-Spam-Score: -1.9 X-Spam-Score-int: -18 X-Spam-Bar: - X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Subject: Re: [bitcoin-dev] Capacity increases for the Bitcoin system. X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Development Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 08 Dec 2015 04:58:10 -0000 > On Mon, Dec 07, 2015 at 10:02:17PM +0000, Gregory Maxwell wrote: > > If widely used this proposal gives a 2x capacity increase > > (more if multisig is widely used), So from IRC, this doesn't seem quite right -- capacity is constrained as base_size + witness_size/4 <= 1MB rather than base_size <= 1MB and base_size + witness_size <= 4MB or similar. So if you have a 500B transaction and move 250B into the witness, you're still using up 250B+250B/4 of the 1MB limit, rather than just 250B of the 1MB limit. In particular, if you use as many p2pkh transactions as possible, you'd have 800kB of base data plus 800kB of witness data, and for a block filled with 2-of-2 multisig p2sh transactions, you'd hit the limit at 670kB of base data and 1.33MB of witness data. That would be 1.6MB and 2MB of total actual data if you hit the limits with real transactions, so it's more like a 1.8x increase for real transactions afaics, even with substantial use of multisig addresses. The 4MB consensus limit could only be hit by having a single trivial transaction using as little base data as possible, then a single huge 4MB witness. So people trying to abuse the system have 4x the blocksize for 1 block's worth of fees, while people using it as intended only get 1.6x or 2x the blocksize... That seems kinda backwards. Having a cost function rather than separate limits does make it easier to build blocks (approximately) optimally, though (ie, just divide the fee by (base_bytes+witness_bytes/4) and sort). Are there any other benefits? But afaics, you could just have fixed consensus limits and use the cost function for building blocks, though? ie sort txs by fee divided by [B + S*50 + W/3] (where B is base bytes, S is sigops and W is witness bytes) then just fill up the block until one of the three limits (1MB base, 20k sigops, 3MB witness) is hit? (Doing a hard fork to make *all* the limits -- base data, witness data, and sigop count -- part of a single cost function might be a win; I'm just not seeing the gain in forcing witness data to trade off against block data when filling blocks is already a 2D knapsack problem) Cheers, aj