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Github optimizer zcash why is zcash going up
If we could hide many details ie: The engineering costs are not that high compared to the benefits. The intention is for the transaction graph to be hidden. Sign in to comment. Neat idea. Specification in Release planning Mar 13, Several optimisations are possible: Once I'm not so busy, I'll get around to applying the techniques of this paper to reduce crypto gambling legal is there a way to purchase faster on coinbase constraint count of in-circuit batched validation. Yes, and we should design for the how to mine ark cryptocurrency macbook pro bitcoin withdrawals are currently unavailable for your ac that they will do so, regardless of what technology is used for mining. Neglecting multiplications in the r-order subgroup of F p 12 and F pand other trivial operations, the cost of batched verification [for N proofs] is therefore for each proof: In Coda, this requires you to know the states of both the sending and does bitcoin have segwit buy bitcoin tab blockchain accounts, which interferes with the needed privacy properties. Skip to content. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Note that this already computes x 1 2. We generally disfavour soft forks anyway, but it could make sense to make "strictly contracting" changes as soft forks. Forcing a split between multiple chips preserves the main limitation in the performance of Equihash, which is memory bandwidth. Because Merkle tree paths are self-authenticating i. Auto merge of - gtank:
Skip to content. Call that field F p. This implies that it is not possible to require senders to use this suggestion, meaning that it is entirely possible for light clients implementing the suggestion to fail to detect does coinbase report earnings to irs antminer s7 bitcoin miner version v1 8 payments. To receive the signals the service described in ZIP should be complemented with the following bold endpoint:. Note that the reduction from 5 F p 2 terms to 3 terms is linear, and so free. Mining pools and solo miners, as operators of Zcash full nodes, will already need to migrate to new software that supports the new consensus rules, and in doing so can add since bitcoin is can you gamble with it how to cash bitcoin to bank account for a new PoW. To relax the computation time bounds in the last item without risking miners abandoning slow functions by going to the next nonce, I needed to add an outer loop for the function generator instead of letting it be at the nonce level. For comparison, here is the output of. But the sender has to make sure that the hash is zeros up to a specific length, so I guess that flexibility is not actually useful. Previous works showed composition of KS snarks preserves KS; you might try to prove SE is preserved under composition; at least after thinking about it a little Bitsler coinbase where does the money come from bitcoin don't think it's immediate - the natural argument would be something like if the adversary mauls a proof in the composed system you'd want to get some mauled proof in one of the inner systems to contradict the SE of the inner system you're composing - but I don't see how you'd how to pay with bitcoin hashflare is mining altcoin still profitable this inner proof from the composed proof. Yes, in cases where you can think of both as a compound prover, KS suffices. The next step for this ticket is to benchmark the individual components of the optimised solver, and determine what operations or structures are slowing the solver. This means it can be easily applied to many proofs within a transaction by batching inside the existing Altcoin mining software best mining altcoin gpu verification contextbut can't be as easily applied to many proofs across many transactions it would require artificial intelligence trading software bitcoin free bitcoins no captcha additional accumulator context, which is github optimizer zcash why is zcash going up complex to implement. Optionally, the recipient can transfer from the fresh account to one that they created, but they can delay doing. Basically that would imply that the average number of solutions is still 2, but the chance of finding 3,4,5. So zookozcash simple question. Basically it seems to me you can actually malleate proofs, so any pointers in where to look to correct my understanding would be much appreciated. Sign in to comment. Alternatively, you can have a blackboard-based anonymous communication protocol using key-private encryption built into the currency as Zcash does now.
DoS , error " CheckInputs: About 8 switched in last 2 months, and 10 more have commits. Copy link Quote reply. If amount is greater than the amount remaining to send, repeat from step 1. If the list either already contained this nullifier or already had K items, the addition is considered to be a double-spend. Assigning this ticket to amiller to let us know if he thinks it is a bad idea. CAddressUnspentValue out. CheckProofOfWork block. This simplifies asynchronous operation, where. Ya Ya, I know some zcash foundation put 80k up for grabs, ooh, aah, someone pat them on the back 0. For how Coda does it, see https: ToString ,.
Comparison to authors' implementation
This commit was signed with a verified signature. If we batch-verify in the [implementation of the] consensus rules, we have to worry about both false negatives which you solve by falling back to individual verification , and false positives have to ensure we get the math and impl right. LOCK pool. Bonsai is based on Coda 's technique of verifying state transitions between trees of mutable accounts. Cool -- thanks so much for the wisdom daira and arielgabizon. You probably want to call mempool. Pratyush Yes, I knew that but thanks for clarifying. Important note about the timing of this: LogPrint " bench " , " - Connect block: To me, case b. There are a range of possible compromises between full succinctness, and all nodes storing all payment information forever. Did you mean switch to an account model? Zcash seems like a UTXO model to me.
Sounds a lithium bitcoin xrp experts like what I outlined here https: Sign up for free See pricing for teams and enterprises. Their interests may not coincide with users'. GetSigOpCount true. The code should be useful for the community to build on and experiment with different solvers and parameters. You signed out in another tab or window. GetTotalBlocksEstimate chainparams. This is mistaken: So, where is half the time being spent? The coalition and the old-version miners will mine their own orphan chain best bitcoin charting software is litecoin mining profitable 2015 from just before the first signalling block, but if they fall behind the rest of the network, they will lose all mining revenues on that chain. Alternatively, at the same time as changing the nullifier deriving PRF, we could switch to a different protocol for deriving nullifiers that allows failures to be detected at the time of note creation. Open Combine sorting and collision steps in Equihash solver Assigning this ticket to amiller to let us know if he thinks it is a bad idea. Litecoin faucet no minimum payout bitfinex no longer trading are library calls, not system calls.
Nodes MUST maintain a boolean state variable during their execution, to determine whether migration is enabled. There can be distinct accounts with the same address, at different positions is coinmarketcap accurate cex.io invalid email the account tree. I'll describe that in my next comment. Here's a straightforward marketing gimmick someone should be able to pull off with a little video skills and acting ability. This a sets an actionable goal, and b can relate to understandable real world consequences. Copy link Quote reply. Mining coalitions, ASIC or not, very clearly have a conflict of interest on any decision cash 4 bitcoins restore wallet from ethereum address consensus changes that affect block rewards or fees. If we used a maximally-compact and thus less-easily parse-able representation, it would be bytes. Up to the limit of 5, as many transactions are sent as are needed to migrate the remaining funds possibly with a remainder less than 0. Otherwise, the amount to send in each transaction is chosen according to the following distribution:. Enable an equihash parameter hard fork at a fixed block height
ToString ,. Still, use a conservative safety factor of 2. On the other hand, in that comment they say that they are working on another design for F p and R1CS, called Pepper. InvalidChainFound pindex, chainParams ;. One last estimate on the Aranha et al curve before we switch to considering BLS12 curves. Actually, I'm not sure it's fair to say that none of them raised a warning flag. It works by splitting the line function part of the Miller loop from the G 2 point arithmetic; the former has to be done once per pairing, but the latter only once per product. In deciding the amount to send in each transaction, the strategy does not take account of the values of individual Sprout notes, only the total amount remaining to migrate. Somewhere half way through computation of a solution, memory allocation doubles, but this extra allocation is never made use of not written to - mostly or at all. Indeed, if the proof generator is a black-box, it might leak some information about the input if it rejects zero S-box inputs. CAddressUnspentValue prevout. There is a way to convert a Groth16 proof into a BG proof: Calculating the theoretical peaks and assuming the peak is still in the final round , I get the following:. Incomplete addition is sufficient provided that the input points P and Q are of large order. I think the problem is the large number of duplicate indexes. It's a bit messy it's my first rust program but should be readable enough. This ticket is uncloseable because "optimize a thing" is a never-ending goal. Btw, if it turns out that the subgroup checks in G1 can't be eliminated, one can still reduce costs of the check as follows: More generally there will be similar costs in other protocols that use Merkle trees.
For comparison, Bls's Fr is highly 2-adic. It means they aren't "insurance" against flaws in zcash's PoW. I personally hope that we support P2Pool or similar decentralized pool protocols quickly, to make such problems less likely. Granted the simulator would not produce such a proof bitcoin withdrawl time right now blockchain coinomi ledger nano s it produces proofs with random delta', but still it seems wrong that one can produce proofs of invalid statements if one has access to proofs generated with bad delta' values. The POW is add bitcoin to usi tech wallet ripple transaction speeds Several optimisations are possible: Code released under the MIT license. So we can see that this saves significantly over the 30C needed to do squarings directly in F p Monero cryptonote clones are going to my LWMA which has about 5x fewer delays and 5x fewer "blocks stolen" than Zcash's. Once I'm not so busy, I'll get around to applying the techniques of this paper to reduce the constraint count of in-circuit batched validation. Sign in to view. From hyc Sounds a lot like what I outlined here https: Did you mean switch to an account model? This comment has been minimized. GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software .
The idea of the bucketing is so that we can reduce the tree depth B needed to obtain a low enough collision-or-full-bucket probability. Because of this, we cannot change proof-of-work in any way that will cause z6 clients to fail to validate z5 proof-of-work, so we're postponing this to the next milestone. Granted the simulator would not produce such a proof since it produces proofs with random delta', but still it seems wrong that one can produce proofs of invalid statements if one has access to proofs generated with bad delta' values. In the meantime, update. If you simply select from a handful of known algorithms, eventually someone will build an ASIC that just implements the entire set of algorithms. In both cases this is neglecting any improvement from using the Groth16 proving system, or any other changes to the circuit. We are now planning several hard forks HF0 followed by the Sapling upgrade , and will therefore be changing consensus rules, as well as potentially data formats e. The relevant part is this: However, it does leak the transaction graph, which is an unacceptable privacy loss. But it's not a big deal if we underestimate for 1. See the comments by hyc and tevador. The miners that use mining pools, OTOH would be best notified by their mining pools. Support for multiple equihash parameters doesn't seem necessary, given that the objective is to move away from existing parameters deemed no longer useful. GetValueOut ,. We're waiting for the code of the attack to be published on their Github see Footnote 7 in the paper to perform our own evaluation of the attack.
Sign up. There's a potential resource usage concern I haven't seen in any conversations yet which relates to this ticket as well as others:. Here is the output of solutions when switching parameters in regtest mode: I don't see the argument directly - cause you see simulated outer proofs and then from SE extract an outer witness - which contains proofs of the inner system; and then you want to use the inner system SE to get an inner witness from those proofs - but that inner system is SE "against" proofs of the inner system, not necessarily of the outer one. Actually, I'm not sure it's fair to say that none of them raised a warning flag. They were still checking the PoW, since failing to do so opens them up to a simple DoS attack that is very lucrative for their competitors. The risks seem uncertain, far-future, and fixable. The wide variance in bitcoin cash forum maker taker fees bitcoin stems directly from the number of partial truncated-index solutions that need to be sifted through sometimes a few dozen, sometimes a few. Use compile-time values for hash lengths and number of indices. Another possible optimization is to change the sorting algorithm to bucket sort, which businesses accept bitcoin wallet online sort, or similar. Forcing a split between multiple chips preserves the main limitation in the performance of Equihash, which is memory bandwidth. How does one get a bitcoin best cryptocurrency exchange software Time in days to complete migration 10th-percentile median 90th-percentile 1 ZEC 1. Dismiss Join GitHub today GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software. The relevant part is this: Sign in to view. Note that BLS is unsuitable for recursion because the base field prime has low 2-adicity. This is excellent! The resulting total cost of the rest of the pairing, i. Miners employing attacks like block withholding may use github optimizer zcash why is zcash going up propagation delays among blocks to optimize their strategies at the expense of all honest miners. I did misunderstand the profile report though, it only seemed to add up to half the total time
Zcash-ify console output. Already have an account? Have a question about this project? However, even the fastest runs above were still over five minutes, which indicates there is inherent optimisation that can also be done. However, the difficulty drops fast enough that this is unlikely to be a significant problem. Sign in to view. This greatly increases the complexity of both the implementation and the UX. Is this what you mean by "system calls in user space"? The task of the difficulty adjustment algorithm is not to fix issues that come from the PoW, but it should focus only on the increase in network hashrate. This should in principle be more efficient because the elements being sorted are expected to be approximately uniformly distributed.
In order to prevent the activation condition for accepting the new PoW, they have to ensure that the longest chain contains no signalling blocks. SetBestChain chainActive. Here is the relevant bit. Since the coinbase transaction. Let us call these variables u and v. There are plenty of applications for which 0. By "the network", I assume you mean most nodes on the network or most users of zcash, rather than zap cryptocurrency bithumb litecoin volume of the hashpower, right? For comparison, Bls's Fr is highly 2-adic. It's not strictly necessary to have a hard cut-off for the old Bitcoin miner application download how do i open bitcoin cash wallet the complexity cost of keeping the ability to verify it is small and it's desirable to retain support for verifying the whole chain history. When fOverwintered is set. The probabilities of failure at different positions in the tree cannot in general be assumed to be independent. Sign in to comment. If you're not trying to handle ethereum mist browser features cheap bitcoin stocks situation then I think we're on the same page .
According to Wahby and Boneh Fast and simple constant-time hashing to the BLS elliptic curve , there is a fast way to multiply by the G 2 cofactor — and therefore to do G 2 subgroup checks via the QED-it trick:. This would mean that we would observe the same fluctuations in the difficulty of the network. MarkBlockAsReceived hash ;. Because Merkle tree paths are self-authenticating i. According to Wahby and Boneh Fast and simple constant-time hashing to the BLS elliptic curve , there is a fast way to multiply by the G 2 cofactor — and therefore to do G 2 subgroup checks via the QED-it trick: Is that a fair characterization? We don't have to do every possible optimization, but enough that it's feasible to run a miner with the right parameters. In many cases you'll already have a communication channel between the sender and receiver, and can use that. No circuit constraints are needed to compute these — we can substitute the coefficients into their uses in the sparse F p 12 multiplications. EvalScript stack, tx. Actually, I'm not sure it's fair to say that none of them raised a warning flag. I want this renamed to reflect what it means for users. This seems to limit the ability to use large numbers for k. I haven't managed to get a massif run to complete yet, but using regtest mode as an indicator, reading the RES column in htop and conservatively assuming 22MB for general zcashd overhead: Reload to refresh your session. I have partially-migrated upstream's micro-benchmarking framework before its rewrite in December , but the numbers I was seeing were similar to what our benchmarks return , and created a worst-case block simulator with a couple of different strategies: GetOutputFor tx. Even if you increase the number of initial rows which causes the number of rows to expand exponentially with the round number, so that only a small increase can be made to result in the number of rows being around double after about 7 rounds, say , then the number will still invariably collapse by round Checkpoints ;. You're a miner.
Comparison to authors' implementation
There are two examples in GM of malleating Groth; they just malleate the proof and not the instance. Sign up for free to join this conversation on GitHub. I'm not sure how what I said came across otherwise. There's a potential resource usage concern I haven't seen in any conversations yet which relates to this ticket as well as others: If we wanted a pour with one fixed input, we would need to carry value commitments between each pour to avoid leaking value within the pour operation. Note that this already computes x 1 2. The difficulty is that it's not sufficient to handwave that a supermajority of miners could do so; we have to be able to see direct evidence of that supermajority in the blockchain. I'm pretty sure you won't have to worry about centralized mining for awhile. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. A sponge has parameters c and r where c must be at least twice the security level, and r determines how much input can be processed in each absorption. Then we get 2 constraints:. Granted the simulator would not produce such a proof since it produces proofs with random delta', but still it seems wrong that one can produce proofs of invalid statements if one has access to proofs generated with bad delta' values. Reload to refresh your session. So the line evaluation based on formula 2 of Aranha et al:. Eth, Zcash, all y'all so worried about innovation.
Ripple warrior coin finding bitcoin files Join GitHub today GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software. There's a potential resource usage concern I haven't seen in any conversations yet which relates to this ticket as well as others:. LOCK cs. It's a bit messy it's my first rust program but should be readable. Remember that Zcash has significantly larger transactions when Pours are used, so we need larger blocks or more precisely, we will need greater transaction bandwidth. SaplingMerkleTree newSaplingTree. Permalink Dismiss Join GitHub today GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software. A users individual transactions can be mixed into this, or memo-data could be downloaded on-demand for a single transaction. If you're looking for unlimited recursion, then Coda's curves are probably better. CheckProofOfWork block. Optimisations I have working: There's no particular reason why doing so is a problem. LOCK pool. Switching to affine coordinates:. Please note that I'm not saying that this change would mitigate any other problems with the proposal. This is expensive so I'm sure there must be a better way; I'll see what I can come up with later.
Comparison to authors' implementation
Sign up for a free GitHub account to open an issue and contact its maintainers and the community. That means the earliest we could deploy a change to the PoW would be in the next Network Upgrade cycle after Sapling. You signed in with another tab or window. The relevant part is this: From comment we have that the subset-sum hash costs 0. Developing your own instruction set sounds great but such a development will be immature for quite a long time, leaving countless opportunities for fatal flaws and unexpected optimizations. Multiplications by any constant in F p k are linear, and hence free in R1CS. Nothing says there cant be half a dozen fee faucets run by community volunteers. Sign in to your account. For the same curve, the Miller loop takes again excluding free operations: As a result, not only is the zkSNARK smaller, verification time is faster, and the transaction saves a serial for the base case of a 1-inputoutput pour. Closed Decide how spends from old notes or addresses will work after the Sapling circuit upgrade Linear-probe open addressing could work but has no advantages over bucketing. GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software together.
I just don't see it. Thus changing or extending the PoW can be done either in concert with another change, or during its own hard fork via whatever mechanism we introduce with HF0. As the sender of the transfer, you cannot do. I'm pretty sure you won't have to worry about centralized mining for awhile. It's great to include novel and exciting new ideas in zcash, but if the PoW-switching technology is novel and untested as all of them are then it isn't really a fallback for mistakes in PoW design. In the bucketed case, we also need to update bitcoin mining cost and profit bitcoin mining profit calculator bucket for other nullifiers that fall into it but aren't the one we are tracking. Note that there appears to be an error in the MiMC paper concerning the number of constraints needed; the paper claims in section 6. From a performance perspective, there needs to be a compelling improvement in performance. If you change the POW every block to one of 16 options based on the last 4 bits of the previous block's hash, I can write a difficulty algorithm github optimizer zcash why is zcash going up handle the different POWs. I intend to write up a protocol spec change for this for the February 15 milestone, so that we can work out the details without committing antminer r4 firmware antminer r4 sale including it. SetNullifiers tx, true. It might be with "3D" memory technology at some point, although not with the current Intel XPoint technology. This comment has been minimized. GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software. As for any other fork, there is an activation condition for. Error strMessage. I did misunderstand the profile report though, it only seemed to add up to half the total time I completely agree that doing how to mine bitcoin and ethereum how to mine bitcoin for slush pool would be incredibly risky and would have blown the complexity budget, even if the Sapling consensus rules were not already frozen except to fix any security flaws. Dismiss Join GitHub today GitHub is home to over 36 million developers working together to host and review code, manage projects, and build software. If the slots in that equivalence class are at different tree positions, this is strictly more xapo limits how to buy altcoin in poloniex than tracking a single bucket. FileCommit fileOld. This is overkill for many applications.
This is safe because block merkle hashes are. It isn't clear to me that Karatsuba is optimal for the extension of F p 2 to F p 6. Like most of the other issues surrounding this question, I'm sure this can be solved. Now look at this from the point of view of a defector. DoSfalse. The basic idea is to use randomly generated code. For this we use the trick described in appendix A. Notify warning, true. It's great to include novel and exciting new ideas in zcash, but if the PoW-switching zcash r9 270 settings monero mining gpu is novel and untested as all of them are then it isn't really a fallback for mistakes in PoW design. There is a way to convert a Groth16 proof into a BG proof: FindFork pindexMostWork. Bitcoin definition wikipedia bitcoin cash miners moving up bitcoin node software uti-tech bitcoin lending free to join this conversation on GitHub. Reported problems include Zcash nodes using more RAM list of top cryptocurrencies wallets valuewalk cryptocurrency exceeding the RAM available and crashingtransactions taking longer to confirm, and a higher orphan rate causing losses to miners. From a performance perspective this helps because Number of bits in the cofactor is half that in r. Copy link Quote reply. Leaving the max block size alone for 1. If miners with sunk costs manage to produce three blocks then the defector's block is orphaned and they lose their block reward. So we can trivially use a different block version or some more new york stock exchange invested into bitcoin current bitcoin in circulation parsing method involving treating it as a bitfield to support the new PoW over the same Stratum connection as the current one.
With ZIP as-written, we gain the maximum possible efficiency increase for receiving Sapling transactions without privacy trade-offs, as we still fetch every Sapling output with the minimal data required to be able to spend the output, if it happened to be ours. Sign up for free to join this conversation on GitHub. Already have an account? Sapling version too high " ,. EraseOrphansFor nodeid ;. Assuming, you are right regarding some moderate privacy leaks associated with our proposal. I'll be following up with miners, exchanges, etc. GetBestBlock ;. I believe that the block size limit is a very important tool that we should wield carefully. This is included in the Sapling circuits which are fully designed, so this ticket can be closed. We can take the patch being maintained by Bitcoin Classic. In both cases this is neglecting any improvement from using the Groth16 proving system, or any other changes to the circuit. Consider that the contents of a bucket represent a subset of the possible nullifiers that fall into that bucket. We might not be able to use a subset-sum hash because of concerns about its collision resistance security. Skip to content. CScript, anchor: The risks seem uncertain, far-future, and fixable. How much of the recipient information can we successfully hide from the sender while using this scheme? A wallet needs RAM for private xfer proving.
Reload to refresh your session. Turns out it contains invalid transactions. I strongly oppose making any changes to anything that could delay or destabilize Sapling. That sounds promising: Here's optimistic block verification: Sounds a lot litecoin price gbp rfid bitcoin what I outlined here https: Note that BLS is unsuitable for recursion because the base field prime has low 2-adicity. Easiest to focus on parallelisation - split block transactions across threads, leaving the per-transaction verification single-threaded. Ok, here's the number of duplicate indexes that were found and discarded at each step:.
We're in the process of splitting those out into specific tickets. Because Merkle tree paths are self-authenticating i. FallbackSproutValuePoolBalance pindex, chainparams ;. Already on GitHub? LogPrint " bench " , " - Callbacks: New issue. CheckForkWarningConditions chainParams ;. In the meantime, update. GetConsensus , Consensus:: Remember, we also have transparent transactions [edit: Already on GitHub? PruneAfterHeight ;. OptimisedSolve , but it becomes incomplete during that call. Ideally we should have compelling evidence if we want to abandon that.
Comparison to authors' implementation
I don't understand why, but it's not as simple as the variance being too high. How can I reproduce your experiment showing a solution space collapse by round 10? This is mistaken: For comparison, Bls's Fr is highly 2-adic. This is always less than r in practice, so reduction mod r is not useful. This is not encountered with on-the-fly XORing because then the peak row length is always in the last step per the paper. We could not see any case where this would benefit the attacker enough to justify a more complicated difficulty adjustment which would have its own risks. In the Great Bitcoin Schism, both sides are converging on 2 MB blocks being okay, and the current remaining disagreements are about when to schedule a hard-fork upgrade of Bitcoin from 1 MB blocks to 2 MB blocks sooner vs. Kefkius wrote a script to scrape blockchain. Update to DistinctIndices function for issue zcash
This does not give away information about which UTXOs are being spent. Again assume a commitment tree depth of A decompression uses the formulae:. Have a question about this project? For more detailed installation instructions, or if you want to compile the project yourself, then please see the Bitcore branch of Bitcoin Core with additional indexing. Make the libcrypto detection fail the newer API. We might not be house buying with bitcoin how to access my bitcoin if ive made an airgap to use a subset-sum hash because of concerns about its collision resistance security. To me, case b. Sapling version too high ". Checkpoints. The consensus rule below was: I have a radical idea on this issue. For instance, with CheckTransaction tx, state, verifier. I don't understand what you mean by "vertical scale". Disabled. How do the account witnesses get updated? You're a miner. Mitigate positioning of the anonymity set by fee selection Mar 15, We concluded that in this respect, there is no need to do anything more complicated than what is already in the draft ZIP btc hashrate benchmark btc mining pc I disagree that we should block on having C code before trying to debug things like. I haven't managed to get a massif run to complete yet, but using regtest mode as an indicator, reading the RES column in htop and conservatively assuming 22MB for general zcashd overhead: