v5.6.0

Change to Transaction Relay Policy

Transactions paying less than the ZIP 317 conventional fee to the extent that they have more than -txunpaidactionlimit unpaid actions (default: 50) will not be accepted to the mempool or relayed. For the default values of -txunpaidactionlimit and -blockunpaidactionlimit, these transactions would never be mined by the ZIP 317 block construction algorithm. (If the transaction has been prioritised by prioritisetransaction, the modified fee is used to calculate the number of unpaid actions.)

Removal of Fee Estimation

The estimatefee RPC call, which estimated the fee needed for a transaction to be included within a target number of blocks, has been removed. The fee that should be paid under normal circumstances is the ZIP 317 conventional fee; it is not possible to compute that without knowing the number of logical actions in a transaction, which was not an input to estimatefee. The fee_estimates.dat file is no longer used.

RPC Changes

A new RPC method, z_getsubtreesbyindex, has been added to the RPC interface. This method is only enabled when running with the -experimentalfeatures=1 and -lightwalletd=1 node configuration options. This method makes available to the caller precomputed node values within the Sapling and Orchard note commitment trees. Wallets can make use of these precomputed values to make their existing notes spendable without needing to fully scan the sub-trees whose roots correspond to the returned node values.

In conjunction with this change, the getblock RPC method now returns an additional trees field as part of its result. The value for this field is an object that contains the final sizes of the Sapling and Orchard note commitment trees after the block's note commitments have been appended to their respective trees.

Error reporting has also been improved for a number of RPC methods.

Privacy Policy Changes

The AllowRevealedSenders privacy policy no longer allows sending from multiple taddrs in the same transaction. This now requires AllowLinkingAccountAddresses. Care should be taken in using AllowLinkingAccountAddresses too broadly, as it can also result in linking UAs when transparent funds are sent from them. The practical effect is that an explicit privacy policy is always required for z_mergetoaddress, z_sendmany, and z_shieldcoinbase when sending from multiple taddrs, even when using wildcards like * and ANY_TADDR.

Wallet Updates

A number of libraries that zcashd relies upon have been updated as part of this release, including some changes that result in updates to wallet serialization formats for Orchard note commitment tree data. As always, it is recommended that users back up their wallets prior to upgrading to a new release to help guarantee the continued availability of their funds.

Platform Support

• Ubuntu 18.04 LTS has been removed from the list of supported platforms. It reached End of Support on May 31st 2023, and no longer satisfies our Tier 2 policy requirements.