tendermint/UPGRADING.md

Upgrading Tendermint Core

This guide provides instructions for upgrading to specific versions of Tendermint Core.

Unreleased

ABCI Changes

• Added AbciVersion to RequestInfo. Applications should check that the ABCI version they expect is being used in order to avoid unimplemented changes errors.
• The method SetOption has been removed from the ABCI.Client interface. This feature was used in the early ABCI implementation's.
• Messages are written to a byte stream using uin64 length delimiters instead of int64.
• When mempool v1 is enabled, transactions broadcasted via sync mode may return a successful response with a transaction hash indicating that the transaction was successfully inserted into the mempool. While this is true for v0, the v1 mempool reactor may at a later point in time evict or even drop this transaction after a hash has been returned. Thus, the user or client must query for that transaction to check if it is still in the mempool.

Config Changes

• fast_sync = "v1" and fast_sync = "v2" are no longer supported. Please use v0 instead.

• All config parameters are now hyphen-case (also known as kebab-case) instead of snake_case. Before restarting the node make sure you have updated all the variables in your config.toml file.

• Added --mode flag and mode config variable on config.toml for setting Mode of the Node: full | validator | seed (default: full) ADR-52

• BootstrapPeers has been added as part of the new p2p stack. This will eventually replace Seeds. Bootstrap peers are connected with on startup if needed for peer discovery. Unlike persistent peers, there's no gaurantee that the node will remain connected with these peers.

• configuration values starting with priv-validator- have moved to the new priv-validator section, without the priv-validator- prefix.

• The fast sync process as well as the blockchain package and service has all been renamed to block sync

Key Format Changes

The format of all tendermint on-disk database keys changes in 0.35. Upgrading nodes must either re-sync all data or run a migration script provided in this release. The script located in github.com/tendermint/tendermint/scripts/keymigrate/migrate.go provides the function Migrate(context.Context, db.DB) which you can operationalize as makes sense for your deployment.

For ease of use the tendermint command includes a CLI version of the migration script, which you can invoke, as in:

tendermint key-migrate

This reads the configuration file as normal and allows the --db-backend and --db-dir flags to change database operations as needed.

The migration operation is idempotent and can be run more than once, if needed.

CLI Changes

• You must now specify the node mode (validator|full|seed) in tendermint init [mode]

• If you had previously used tendermint gen_node_key to generate a new node key, keep in mind that it no longer saves the output to a file. You can use tendermint init validator or pipe the output of tendermint gen_node_key to $TMHOME/config/node_key.json:

  $ tendermint gen_node_key > $TMHOME/config/node_key.json
  

• CLI commands and flags are all now hyphen-case instead of snake_case. Make sure to adjust any scripts that calls a cli command with snake_casing

API Changes

The p2p layer was reimplemented as part of the 0.35 release cycle, and all reactors were refactored. As part of that work these implementations moved into the internal package and are no longer considered part of the public Go API of tendermint. These packages are:

• p2p
• mempool
• consensus
• statesync
• blockchain
• evidence

Accordingly, the node package was changed to reduce access to tendermint internals: applications that use tendermint as a library will need to change to accommodate these changes. Most notably:

• The Node type has become internal, and all constructors return a service.Service implementation.

• The node.DefaultNewNode and node.NewNode constructors are no longer exported and have been replaced with node.New and node.NewDefault which provide more functional interfaces.

RPC changes

gRPC Support

Mark gRPC in the RPC layer as deprecated and to be removed in 0.36.

Peer Management Interface

When running with the new P2P Layer, the methods UnsafeDialSeeds and UnsafeDialPeers RPC methods will always return an error. They are deprecated and will be removed in 0.36 when the legacy peer stack is removed.

Additionally the format of the Peer list returned in the NetInfo method changes in this release to accommodate the different way that the new stack tracks data about peers. This change affects users of both stacks.

Support for Custom Reactor and Mempool Implementations

The changes to p2p layer removed existing support for custom reactors. Based on our understanding of how this functionality was used, the introduction of the prioritized mempool covers nearly all of the use cases for custom reactors. If you are currently running custom reactors and mempools and are having trouble seeing the migration path for your project please feel free to reach out to the Tendermint Core development team directly.

v0.34.0

Upgrading to Tendermint 0.34 requires a blockchain restart. This release is not compatible with previous blockchains due to changes to the encoding format (see "Protocol Buffers," below) and the block header (see "Blockchain Protocol").

Note also that Tendermint 0.34 also requires Go 1.16 or higher.

ABCI Changes

• The ABCIVersion is now 0.17.0.

• New ABCI methods (ListSnapshots, LoadSnapshotChunk, OfferSnapshot, and ApplySnapshotChunk) were added to support the new State Sync feature. Previously, syncing a new node to a preexisting network could take days; but with State Sync, new nodes are able to join a network in a matter of seconds. Read the spec if you want to learn more about State Sync, or if you'd like your application to use it. (If you don't want to support State Sync in your application, you can just implement these new ABCI methods as no-ops, leaving them empty.)

• KV.Pair has been replaced with abci.EventAttribute. The EventAttribute.Index field allows ABCI applications to dictate which events should be indexed.

• The blockchain can now start from an arbitrary initial height, provided to the application via RequestInitChain.InitialHeight.

• ABCI evidence type is now an enum with two recognized types of evidence: DUPLICATE_VOTE and LIGHT_CLIENT_ATTACK. Applications should be able to handle these evidence types (i.e., through slashing or other accountability measures).

• The PublicKey type (used in ABCI as part of ValidatorUpdate) now uses a oneof protobuf type. Note that since Tendermint only supports ed25519 validator keys, there's only one option in the oneof. For more, see "Protocol Buffers," below.

• The field Proof, on the ABCI type ResponseQuery, is now named ProofOps. For more, see "Crypto," below.

• The method SetOption has been removed from the ABCI.Client interface. This feature was used in the early ABCI implementation's.

P2P Protocol

The default codec is now proto3, not amino. The schema files can be found in the /proto directory. For more, see "Protobuf," below.

Blockchain Protocol

• Header#LastResultsHash, which is the root hash of a Merkle tree built from ResponseDeliverTx(Code, Data) as of v0.34 also includes GasWanted and GasUsed fields.

• Merkle hashes of empty trees previously returned nothing, but now return the hash of an empty input, to conform with RFC-6962. This mainly affects Header#DataHash, Header#LastResultsHash, and Header#EvidenceHash, which are often empty. Non-empty hashes can also be affected, e.g. if their inputs depend on other (empty) Merkle hashes, giving different results.

Transaction Indexing

Tendermint now relies on the application to tell it which transactions to index. This means that in the config.toml, generated by Tendermint, there is no longer a way to specify which transactions to index. tx.height and tx.hash will always be indexed when using the kv indexer.

Applications must now choose to either a) enable indexing for all transactions, or b) allow node operators to decide which transactions to index. Applications can notify Tendermint to index a specific transaction by setting Index: bool to true in the Event Attribute:

[]types.Event{
	{
		Type: "app",
		Attributes: []types.EventAttribute{
			{Key: []byte("creator"), Value: []byte("Cosmoshi Netowoko"), Index: true},
		},
	},
}

Protocol Buffers

Tendermint 0.34 replaces Amino with Protocol Buffers for encoding. This migration is extensive and results in a number of changes, however, Tendermint only uses the types generated from Protocol Buffers for disk and wire serialization. This means that these changes should not affect you as a Tendermint user.

However, Tendermint users and contributors may note the following changes:

• Directory layout changes: All proto files have been moved under one directory, /proto. This is in line with the recommended file layout by Buf. For more, see the Buf documentation.
• ABCI Changes: As noted in the "ABCI Changes" section above, the PublicKey type now uses a oneof type.

For more on the Protobuf changes, please see our blog post on this migration.

Consensus Parameters

Tendermint 0.34 includes new and updated consensus parameters.

Version Parameters (New)

• AppVersion, which is the version of the ABCI application.

Evidence Parameters

• MaxBytes, which caps the total amount of evidence. The default is 1048576 (1 MB).

Crypto

Keys

• Keys no longer include a type prefix. For example, ed25519 pubkeys have been renamed from PubKeyEd25519 to PubKey. This reduces stutter (e.g., ed25519.PubKey).
• Keys are now byte slices ([]byte) instead of byte arrays ([<size>]byte).
• The multisig functionality that was previously in Tendermint now has a new home within the Cosmos SDK: cosmos/cosmos-sdk/types/multisig.

merkle Package

• SimpleHashFromMap() and SimpleProofsFromMap() were removed.
• The prefix Simple has been removed. (For example, SimpleProof is now called Proof.)
• All protobuf messages have been moved to the /proto directory.
• The protobuf message Proof that contained multiple ProofOp's has been renamed to ProofOps. As noted above, this affects the ABCI type ResponseQuery: The field that was named Proof is now named ProofOps.
• HashFromByteSlices and ProofsFromByteSlices now return a hash for empty inputs, to conform with RFC-6962.

libs Package

The bech32 package has moved to the Cosmos SDK: cosmos/cosmos-sdk/types/bech32.

CLI

The tendermint lite command has been renamed to tendermint light and has a slightly different API. See the docs for details.

Light Client

We have a new, rewritten light client! You can read more about the justifications and details behind this change.

Other user-relevant changes include:

• The old lite package was removed; the new light client uses the light package.
• The Verifier was broken up into two pieces:
  • Core verification logic (pure VerifyX functions)
  • Client object, which represents the complete light client
• The new light clients stores headers & validator sets as LightBlocks
• The RPC client can be found in the /rpc directory.
• The HTTP(S) proxy is located in the /proxy directory.

state Package

• A new field State.InitialHeight has been added to record the initial chain height, which must be 1 (not 0) if starting from height 1. This can be configured via the genesis field initial_height.
• The state package now has a Store interface. All functions in state/store.go are now part of the interface. The interface returns errors on all methods and can be used by calling state.NewStore(dbm.DB).

privval Package

All requests are now accompanied by the chain ID from the network. This is a optional field and can be ignored by key management systems; however, if you are using the same key management system for multiple different blockchains, we recommend that you check the chain ID.

RPC

• /unsafe_start_cpu_profiler, /unsafe_stop_cpu_profiler and /unsafe_write_heap_profile were removed. For profiling, please use the pprof server, which can be enabled through --rpc.pprof_laddr=X flag or pprof_laddr=X config setting in the rpc section.
• The Content-Type header returned on RPC calls is now (correctly) set as application/json.

Version

Version is now set through Go linker flags ld_flags. Applications that are using tendermint as a library should set this at compile time.

Example:

go install -mod=readonly -ldflags "-X github.com/tendermint/tendermint/version.TMCoreSemVer=$(go list -m github.com/tendermint/tendermint | sed  's/ /\@/g') -s -w " -trimpath ./cmd

Additionally, the exported constant version.Version is now version.TMCoreSemVer.

v0.33.4

Go API

• rpc/client HTTP and local clients have been moved into http and local subpackages, and their constructors have been renamed to New().

Protobuf Changes

When upgrading to version 0.33.4 you will have to fetch the third_party directory along with the updated proto files.

Block Retention

ResponseCommit added a field for block retention. The application can provide information to Tendermint on how to prune blocks. If an application would like to not prune any blocks pass a 0 in this field.

message ResponseCommit {
  // reserve 1
  bytes  data          = 2; // the Merkle root hash
  ++ uint64 retain_height = 3; // the oldest block height to retain ++
}

v0.33.0

This release is not compatible with previous blockchains due to commit becoming signatures only and fields in the header have been removed.

Blockchain Protocol

TotalTxs and NumTxs were removed from the header. Commit now consists mostly of just signatures.

type Commit struct {
	Height     int64
	Round      int
	BlockID    BlockID
	Signatures []CommitSig
}

type BlockIDFlag byte

const (
	// BlockIDFlagAbsent - no vote was received from a validator.
	BlockIDFlagAbsent BlockIDFlag = 0x01
	// BlockIDFlagCommit - voted for the Commit.BlockID.
	BlockIDFlagCommit = 0x02
	// BlockIDFlagNil - voted for nil.
	BlockIDFlagNil = 0x03
)

type CommitSig struct {
	BlockIDFlag      BlockIDFlag
	ValidatorAddress Address
	Timestamp        time.Time
	Signature        []byte
}

See #63 for the complete spec change.

P2P Protocol

The secret connection now includes a transcript hashing. If you want to implement a handshake (or otherwise have an existing implementation), you'll need to make the same changes that were made here.

Config Changes

You will need to generate a new config if you have used a prior version of tendermint.

Tags have been entirely renamed throughout the codebase to events and there keys are called compositeKeys.

Evidence Params has been changed to include duration.

• consensus_params.evidence.max_age_duration.
• Renamed consensus_params.evidence.max_age to max_age_num_blocks.

Go API

• libs/common has been removed in favor of specific pkgs.
  • async
  • service
  • rand
  • net
  • strings
  • cmap
• removal of errors pkg

RPC Changes

• /validators is now paginated (default: 30 vals per page)
• /block_results response format updated see RPC docs for details
• Event suffix has been removed from the ID in event responses
• IDs are now integers not json-client-XYZ

v0.32.0

This release is compatible with previous blockchains, however the new ABCI Events mechanism may create some complexity for nodes wishing to continue operation with v0.32 from a previous version. There are some minor breaking changes to the RPC.

Config Changes

If you have db_backend set to leveldb in your config file, please change it to goleveldb or cleveldb.

RPC Changes

The default listen address for the RPC is now 127.0.0.1. If you want to expose it publicly, you have to explicitly configure it. Note exposing the RPC to the public internet may not be safe - endpoints which return a lot of data may enable resource exhaustion attacks on your node, causing the process to crash.

Any consumers of /block_results need to be mindful of the change in all field names from CamelCase to Snake case, eg. results.DeliverTx is now results.deliver_tx. This is a fix, but it's breaking.

ABCI Changes

ABCI responses which previously had a Tags field now have an Events field instead. The original Tags field was simply a list of key-value pairs, where each key effectively represented some attribute of an event occuring in the blockchain, like sender, receiver, or amount. However, it was difficult to represent the occurence of multiple events (for instance, multiple transfers) in a single list. The new Events field contains a list of Event, where each Event is itself a list of key-value pairs, allowing for more natural expression of multiple events in eg. a single DeliverTx or EndBlock. Note each Event also includes a Type, which is meant to categorize the event.

For transaction indexing, the index key is prefixed with the event type: {eventType}.{attributeKey}. If the same event type and attribute key appear multiple times, the values are appended in a list.

To make queries, include the event type as a prefix. For instance if you previously queried for recipient = 'XYZ', and after the upgrade you name your event transfer, the new query would be for transfer.recipient = 'XYZ'.

Note that transactions indexed on a node before upgrading to v0.32 will still be indexed using the old scheme. For instance, if a node upgraded at height 100, transactions before 100 would be queried with recipient = 'XYZ' and transactions after 100 would be queried with transfer.recipient = 'XYZ'. While this presents additional complexity to clients, it avoids the need to reindex. Of course, you can reset the node and sync from scratch to re-index entirely using the new scheme.

We illustrate further with a more complete example.

Prior to the update, suppose your ResponseDeliverTx look like:

abci.ResponseDeliverTx{
  Tags: []kv.Pair{
	{Key: []byte("sender"), Value: []byte("foo")},
	{Key: []byte("recipient"), Value: []byte("bar")},
	{Key: []byte("amount"), Value: []byte("35")},
  }
}

The following queries would match this transaction:

query.MustParse("tm.event = 'Tx' AND sender = 'foo'")
query.MustParse("tm.event = 'Tx' AND recipient = 'bar'")
query.MustParse("tm.event = 'Tx' AND sender = 'foo' AND recipient = 'bar'")

Following the upgrade, your ResponseDeliverTx would look something like: the following Events:

abci.ResponseDeliverTx{
  Events: []abci.Event{
	{
	  Type: "transfer",
	  Attributes: kv.Pairs{
		{Key: []byte("sender"), Value: []byte("foo")},
		{Key: []byte("recipient"), Value: []byte("bar")},
		{Key: []byte("amount"), Value: []byte("35")},
	  },
	}
}

Now the following queries would match this transaction:

query.MustParse("tm.event = 'Tx' AND transfer.sender = 'foo'")
query.MustParse("tm.event = 'Tx' AND transfer.recipient = 'bar'")
query.MustParse("tm.event = 'Tx' AND transfer.sender = 'foo' AND transfer.recipient = 'bar'")

For further documentation on Events, see the docs.

Go Applications

The ABCI Application interface changed slightly so the CheckTx and DeliverTx methods now take Request structs. The contents of these structs are just the raw tx bytes, which were previously passed in as the argument.

v0.31.6

There are no breaking changes in this release except Go API of p2p and mempool packages. Hovewer, if you're using cleveldb, you'll need to change the compilation tag:

Use cleveldb tag instead of gcc to compile Tendermint with CLevelDB or use make build_c / make install_c (full instructions can be found at https://tendermint.com/docs/introduction/install.html#compile-with-cleveldb-support)

v0.31.0

This release contains a breaking change to the behaviour of the pubsub system. It also contains some minor breaking changes in the Go API and ABCI. There are no changes to the block or p2p protocols, so v0.31.0 should work fine with blockchains created from the v0.30 series.

RPC

The pubsub no longer blocks on publishing. This may cause some WebSocket (WS) clients to stop working as expected. If your WS client is not consuming events fast enough, Tendermint can terminate the subscription. In this case, the WS client will receive an error with description:

{
  "jsonrpc": "2.0",
  "id": "{ID}#event",
  "error": {
	"code": -32000,
	"msg": "Server error",
	"data": "subscription was canceled (reason: client is not pulling messages fast enough)" // or "subscription was canceled (reason: Tendermint exited)"
  }
}

Additionally, there are now limits on the number of subscribers and
subscriptions that can be active at once. See the new
`rpc.max_subscription_clients` and `rpc.max_subscriptions_per_client` values to
configure this.

Applications

Simple rename of ConsensusParams.BlockSize to ConsensusParams.Block.

The ConsensusParams.Block.TimeIotaMS field was also removed. It's configured in the ConsensusParsm in genesis.

Go API

See the CHANGELOG. These are relatively straight forward.

v0.30.0

This release contains a breaking change to both the block and p2p protocols, however it may be compatible with blockchains created with v0.29.0 depending on the chain history. If your blockchain has not included any pieces of evidence, or no piece of evidence has been included in more than one block, and if your application has never returned multiple updates for the same validator in a single block, then v0.30.0 will work fine with blockchains created with v0.29.0.

The p2p protocol change is to fix the proposer selection algorithm again. Note that proposer selection is purely a p2p concern right now since the algorithm is only relevant during real time consensus. This change is thus compatible with v0.29.0, but all nodes must be upgraded to avoid disagreements on the proposer.

Applications

Applications must ensure they do not return duplicates in ResponseEndBlock.ValidatorUpdates. A pubkey must only appear once per set of updates. Duplicates will cause irrecoverable failure. If you have a very good reason why we shouldn't do this, please open an issue.

v0.29.0

This release contains some breaking changes to the block and p2p protocols, and will not be compatible with any previous versions of the software, primarily due to changes in how various data structures are hashed.

Any implementations of Tendermint blockchain verification, including lite clients, will need to be updated. For specific details:

• Merkle tree
• ConsensusParams

There was also a small change to field ordering in the vote struct. Any implementations of an out-of-process validator (like a Key-Management Server) will need to be updated. For specific details:

• Vote

Finally, the proposer selection algorithm continues to evolve. See the work-in-progress specification.

For everything else, please see the CHANGELOG.

v0.28.0

This release breaks the format for the priv_validator.json file and the protocol used for the external validator process. It is compatible with v0.27.0 blockchains (neither the BlockProtocol nor the P2PProtocol have changed).

Please read carefully for details about upgrading.

Note: Backup your config/priv_validator.json before proceeding.

priv_validator.json

The config/priv_validator.json is now two files: config/priv_validator_key.json and data/priv_validator_state.json. The former contains the key material, the later contains the details on the last message signed.

When running v0.28.0 for the first time, it will back up any pre-existing priv_validator.json file and proceed to split it into the two new files. Upgrading should happen automatically without problem.

To upgrade manually, use the provided privValUpgrade.go script, with exact paths for the old priv_validator.json and the locations for the two new files. It's recomended to use the default paths, of config/priv_validator_key.json and data/priv_validator_state.json, respectively:

go run scripts/privValUpgrade.go <old-path> <new-key-path> <new-state-path>

External validator signers

The Unix and TCP implementations of the remote signing validator have been consolidated into a single implementation. Thus in both cases, the external process is expected to dial Tendermint. This is different from how Unix sockets used to work, where Tendermint dialed the external process.

The PubKeyMsg was also split into separate Request and Response types for consistency with other messages.

Note that the TCP sockets don't yet use a persistent key, so while they're encrypted, they can't yet be properly authenticated. See #3105. Note the Unix socket has neither encryption nor authentication, but will add a shared-secret in #3099.

v0.27.0

This release contains some breaking changes to the block and p2p protocols, but does not change any core data structures, so it should be compatible with existing blockchains from the v0.26 series that only used Ed25519 validator keys. Blockchains using Secp256k1 for validators will not be compatible. This is due to the fact that we now enforce which key types validators can use as a consensus param. The default is Ed25519, and Secp256k1 must be activated explicitly.

It is recommended to upgrade all nodes at once to avoid incompatibilities at the peer layer - namely, the heartbeat consensus message has been removed (only relevant if create_empty_blocks=false or create_empty_blocks_interval > 0), and the proposer selection algorithm has changed. Since proposer information is never included in the blockchain, this change only affects the peer layer.

Go API Changes

libs/db

The ReverseIterator API has changed the meaning of start and end. Before, iteration was from start to end, where start > end. Now, iteration is from end to start, where start < end. The iterator also excludes end. This change allows a simplified and more intuitive logic, aligning the semantic meaning of start and end in the Iterator and ReverseIterator.

Applications

This release enforces a new consensus parameter, the ValidatorParams.PubKeyTypes. Applications must ensure that they only return validator updates with the allowed PubKeyTypes. If a validator update includes a pubkey type that is not included in the ConsensusParams.Validator.PubKeyTypes, block execution will fail and the consensus will halt.

By default, only Ed25519 pubkeys may be used for validators. Enabling Secp256k1 requires explicit modification of the ConsensusParams. Please update your application accordingly (ie. restrict validators to only be able to use Ed25519 keys, or explicitly add additional key types to the genesis file).

v0.26.0

This release contains a lot of changes to core data types and protocols. It is not compatible to the old versions and there is no straight forward way to update old data to be compatible with the new version.

To reset the state do:

tendermint unsafe_reset_all

Here we summarize some other notable changes to be mindful of.

Config Changes

All timeouts must be changed from integers to strings with their duration, for instance flush_throttle_timeout = 100 would be changed to flush_throttle_timeout = "100ms" and timeout_propose = 3000 would be changed to timeout_propose = "3s".

RPC Changes

The default behaviour of /abci_query has been changed to not return a proof, and the name of the parameter that controls this has been changed from trusted to prove. To get proofs with your queries, ensure you set prove=true.

Various version fields like amino_version, p2p_version, consensus_version, and rpc_version have been removed from the node_info.other and are consolidated under the tendermint semantic version (ie. node_info.version) and the new block and p2p protocol versions under node_info.protocol_version.

ABCI Changes

Field numbers were bumped in the Header and ResponseInfo messages to make room for new version fields. It should be straight forward to recompile the protobuf file for these changes.

Proofs

The ResponseQuery.Proof field is now structured as a []ProofOp to support generalized Merkle tree constructions where the leaves of one Merkle tree are the root of another. If you don't need this functionality, and you used to return <proof bytes> here, you should instead return a single ProofOp with just the Data field set:

[]ProofOp{
	ProofOp{
		Data: <proof bytes>,
	}
}

For more information, see:

• ADR-026
• Relevant ABCI documentation
• Description of keys

Go API Changes

crypto/merkle

The merkle.Hasher interface was removed. Functions which used to take Hasher now simply take []byte. This means that any objects being Merklized should be serialized before they are passed in.

node

The node.RunForever function was removed. Signal handling and running forever should instead be explicitly configured by the caller. See how we do it here.

Other

All hashes, except for public key addresses, are now 32-bytes.

v0.25.0

This release has minimal impact.

If you use GasWanted in ABCI and want to enforce it, set the MaxGas in the genesis file (default is no max).

v0.24.0

New 0.24.0 release contains a lot of changes to the state and types. It's not compatible to the old versions and there is no straight forward way to update old data to be compatible with the new version.

To reset the state do:

tendermint unsafe_reset_all

Here we summarize some other notable changes to be mindful of.

Config changes

p2p.max_num_peers was removed in favor of p2p.max_num_inbound_peers and p2p.max_num_outbound_peers.

# Maximum number of inbound peers
max_num_inbound_peers = 40

# Maximum number of outbound peers to connect to, excluding persistent peers
max_num_outbound_peers = 10

As you can see, the default ratio of inbound/outbound peers is 4/1. The reason is we want it to be easier for new nodes to connect to the network. You can tweak these parameters to alter the network topology.

RPC Changes

The result of /commit used to contain header and commit fields at the top level. These are now contained under the signed_header field.

ABCI Changes

The header has been upgraded and contains new fields, but none of the existing fields were changed, except their order.

The Validator type was split into two, one containing an Address and one containing a PubKey. When processing RequestBeginBlock, use the Validator type, which contains just the Address. When returning ResponseEndBlock, use the ValidatorUpdate type, which contains just the PubKey.

Validator Set Updates

Validator set updates returned in ResponseEndBlock for height H used to take effect immediately at height H+1. Now they will be delayed one block, to take effect at height H+2. Note this means that the change will be seen by the ABCI app in the RequestBeginBlock.LastCommitInfo at block H+3. Apps were already required to maintain a map from validator addresses to pubkeys since v0.23 (when pubkeys were removed from RequestBeginBlock), but now they may need to track multiple validator sets at once to accomodate this delay.

Block Size

The ConsensusParams.BlockSize.MaxTxs was removed in favour of ConsensusParams.BlockSize.MaxBytes, which is now enforced. This means blocks are limitted only by byte-size, not by number of transactions.