Auto merge of zcash#3002 - str4d:2957-overwinter-release-notes, r=str4d

Overwinter release notes and testnet activation height

Closes zcash#2957.

doc/release-notes.md

@@ -4,6 +4,41 @@ release-notes at release time)
 Notable changes
 ===============
 
+Overwinter network upgrade
+--------------------------
+
+The code preparations for the Overwinter network upgrade, as described in [ZIP
+200](https://github.com/zcash/zips/blob/master/zip-0200.rst), [ZIP
+201](https://github.com/zcash/zips/blob/master/zip-0201.rst), [ZIP
+202](https://github.com/zcash/zips/blob/master/zip-0202.rst), [ZIP
+203](https://github.com/zcash/zips/blob/master/zip-0203.rst), and [ZIP
+143](https://github.com/zcash/zips/blob/master/zip-0143.rst) are
+finished and included in this release. Overwinter will activate on testnet at
+height 207500, and can also be activated at a specific height in regtest mode
+by setting the config option `-nuparams=5ba81b19:HEIGHT`.
+
+However, because the Overwinter activation height is not yet specified for
+mainnet, version 1.0.15 will behave similarly as other pre-Overwinter releases
+even after a future activation of Overwinter on the network. Upgrading from
+1.0.15 will be required in order to follow the Overwinter network upgrade on
+mainnet.
+
+Overwinter transaction format
+-----------------------------
+
+Once Overwinter has activated, transactions must use the new v3 format
+(including coinbase transactions). All RPC methods that create new transactions
+(such as `createrawtransaction` and `getblocktemplate`) will create v3
+transactions once the Overwinter activation height has been reached.
+
+Overwinter transaction expiry
+-----------------------------
+
+Overwinter transactions created by `zcashd` will also have a default expiry
+height set (the block height after which the transaction becomes invalid) of 20
+blocks after the height of the next block. This can be configured with the
+config option `-txexpirydelta`.
+
 UTXO and note merging
 ---------------------
 
@@ -24,6 +59,10 @@ merging until the number of UTXOs falls below some value).
 UTXO memory accounting
 ----------------------
 
-The default -dbcache has been changed in this release to 450MiB. Users can set -dbcache to a higher value (e.g. to keep the UTXO set more fully cached in memory). Users on low-memory systems (such as systems with 1GB or less) should consider specifying a lower value for this parameter.
+The default `-dbcache` has been changed in this release to 450MiB. Users can set
+`-dbcache` to a higher value (e.g. to keep the UTXO set more fully cached in
+memory). Users on low-memory systems (such as systems with 1GB or less) should
+consider specifying a lower value for this parameter.
 
-Additional information relating to running on low-memory systems can be found here: [reducing-memory-usage.md](https://github.com/zcash/zcash/blob/master/doc/reducing-memory-usage.md).
+Additional information relating to running on low-memory systems can be found
+here: [reducing-memory-usage.md](https://github.com/zcash/zcash/blob/master/doc/reducing-memory-usage.md).

src/chainparams.cpp

@@ -263,8 +263,7 @@ class CTestNetParams : public CChainParams {
         consensus.vUpgrades[Consensus::UPGRADE_TESTDUMMY].nActivationHeight =
             Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
         consensus.vUpgrades[Consensus::UPGRADE_OVERWINTER].nProtocolVersion = 170003;
-        consensus.vUpgrades[Consensus::UPGRADE_OVERWINTER].nActivationHeight =
-            Consensus::NetworkUpgrade::NO_ACTIVATION_HEIGHT;
+        consensus.vUpgrades[Consensus::UPGRADE_OVERWINTER].nActivationHeight = 207500;
 
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0x1a;