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docs/spec: some organizational cleanup

pull/1757/head
Ethan Buchman 6 years ago
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8 changed files with 247 additions and 478 deletions
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  1. +11
    -7
      docs/spec/README.md
  2. +0
    -246
      docs/spec/blockchain/pre-amino.md
  3. +1
    -192
      docs/spec/consensus/abci.md
  4. +9
    -0
      docs/spec/consensus/consensus.md
  5. +0
    -0
      docs/spec/consensus/light-client.md
  6. +1
    -33
      docs/spec/consensus/wal.md
  7. +192
    -0
      docs/spec/software/abci.md
  8. +33
    -0
      docs/spec/software/wal.md

+ 11
- 7
docs/spec/README.md View File

@ -20,7 +20,9 @@ please submit them to our [bug bounty](https://tendermint.com/security)!
### Consensus Protocol
- TODO
- [Consensus Algorithm](/docs/spec/consensus/consensus.md)
- [Time](/docs/spec/consensus/bft-time.md)
- [Light-Client](/docs/spec/consensus/light-client.md)
### P2P and Network Protocols
@ -31,9 +33,12 @@ please submit them to our [bug bounty](https://tendermint.com/security)!
- [Mempool](https://github.com/tendermint/tendermint/tree/master/docs/spec/reactors/mempool): gossip transactions so they get included in blocks
- Evidence: TODO
### More
- Light Client: TODO
- Persistence: TODO
### Software
- [ABCI](/docs/spec/software/abci.md): Details about interactions between the
application and consensus engine over ABCI
- [Write-Ahead Log](/docs/spec/software/wal.md): Details about how the consensus
engine preserves data and recovers from crash failures
## Overview
@ -42,10 +47,9 @@ hash-linked batches of transactions. Such transaction batches are called "blocks
Hence, Tendermint defines a "blockchain".
Each block in Tendermint has a unique index - its Height.
A block at `Height == H` can only be committed *after* the
block at `Height == H-1`.
Height's in the blockchain are monotonic.
Each block is committed by a known set of weighted Validators.
Membership and weighting within this set may change over time.
Membership and weighting within this validator set may change over time.
Tendermint guarantees the safety and liveness of the blockchain
so long as less than 1/3 of the total weight of the Validator set
is malicious or faulty.


+ 0
- 246
docs/spec/blockchain/pre-amino.md View File

@ -1,246 +0,0 @@
# Tendermint Encoding (Pre-Amino)
## PubKeys and Addresses
PubKeys are prefixed with a type-byte, followed by the raw bytes of the public
key.
Two keys are supported with the following type bytes:
```
TypeByteEd25519 = 0x1
TypeByteSecp256k1 = 0x2
```
```
// TypeByte: 0x1
type PubKeyEd25519 [32]byte
func (pub PubKeyEd25519) Encode() []byte {
return 0x1 | pub
}
func (pub PubKeyEd25519) Address() []byte {
// NOTE: the length (0x0120) is also included
return RIPEMD160(0x1 | 0x0120 | pub)
}
// TypeByte: 0x2
// NOTE: OpenSSL compressed pubkey (x-cord with 0x2 or 0x3)
type PubKeySecp256k1 [33]byte
func (pub PubKeySecp256k1) Encode() []byte {
return 0x2 | pub
}
func (pub PubKeySecp256k1) Address() []byte {
return RIPEMD160(SHA256(pub))
}
```
See https://github.com/tendermint/go-crypto/blob/v0.5.0/pub_key.go for more.
## Binary Serialization (go-wire)
Tendermint aims to encode data structures in a manner similar to how the corresponding Go structs
are laid out in memory.
Variable length items are length-prefixed.
While the encoding was inspired by Go, it is easily implemented in other languages as well, given its intuitive design.
XXX: This is changing to use real varints and 4-byte-prefixes.
See https://github.com/tendermint/go-wire/tree/sdk2.
### Fixed Length Integers
Fixed length integers are encoded in Big-Endian using the specified number of bytes.
So `uint8` and `int8` use one byte, `uint16` and `int16` use two bytes,
`uint32` and `int32` use 3 bytes, and `uint64` and `int64` use 4 bytes.
Negative integers are encoded via twos-complement.
Examples:
```go
encode(uint8(6)) == [0x06]
encode(uint32(6)) == [0x00, 0x00, 0x00, 0x06]
encode(int8(-6)) == [0xFA]
encode(int32(-6)) == [0xFF, 0xFF, 0xFF, 0xFA]
```
### Variable Length Integers
Variable length integers are encoded as length-prefixed Big-Endian integers.
The length-prefix consists of a single byte and corresponds to the length of the encoded integer.
Negative integers are encoded by flipping the leading bit of the length-prefix to a `1`.
Zero is encoded as `0x00`. It is not length-prefixed.
Examples:
```go
encode(uint(6)) == [0x01, 0x06]
encode(uint(70000)) == [0x03, 0x01, 0x11, 0x70]
encode(int(-6)) == [0xF1, 0x06]
encode(int(-70000)) == [0xF3, 0x01, 0x11, 0x70]
encode(int(0)) == [0x00]
```
### Strings
An encoded string is length-prefixed followed by the underlying bytes of the string.
The length-prefix is itself encoded as an `int`.
The empty string is encoded as `0x00`. It is not length-prefixed.
Examples:
```go
encode("") == [0x00]
encode("a") == [0x01, 0x01, 0x61]
encode("hello") == [0x01, 0x05, 0x68, 0x65, 0x6C, 0x6C, 0x6F]
encode("¥") == [0x01, 0x02, 0xC2, 0xA5]
```
### Arrays (fixed length)
An encoded fix-lengthed array is the concatenation of the encoding of its elements.
There is no length-prefix.
Examples:
```go
encode([4]int8{1, 2, 3, 4}) == [0x01, 0x02, 0x03, 0x04]
encode([4]int16{1, 2, 3, 4}) == [0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x04]
encode([4]int{1, 2, 3, 4}) == [0x01, 0x01, 0x01, 0x02, 0x01, 0x03, 0x01, 0x04]
encode([2]string{"abc", "efg"}) == [0x01, 0x03, 0x61, 0x62, 0x63, 0x01, 0x03, 0x65, 0x66, 0x67]
```
### Slices (variable length)
An encoded variable-length array is length-prefixed followed by the concatenation of the encoding of
its elements.
The length-prefix is itself encoded as an `int`.
An empty slice is encoded as `0x00`. It is not length-prefixed.
Examples:
```go
encode([]int8{}) == [0x00]
encode([]int8{1, 2, 3, 4}) == [0x01, 0x04, 0x01, 0x02, 0x03, 0x04]
encode([]int16{1, 2, 3, 4}) == [0x01, 0x04, 0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0x00, 0x04]
encode([]int{1, 2, 3, 4}) == [0x01, 0x04, 0x01, 0x01, 0x01, 0x02, 0x01, 0x03, 0x01, 0x4]
encode([]string{"abc", "efg"}) == [0x01, 0x02, 0x01, 0x03, 0x61, 0x62, 0x63, 0x01, 0x03, 0x65, 0x66, 0x67]
```
### BitArray
BitArray is encoded as an `int` of the number of bits, and with an array of `uint64` to encode
value of each array element.
```go
type BitArray struct {
Bits int
Elems []uint64
}
```
### Time
Time is encoded as an `int64` of the number of nanoseconds since January 1, 1970,
rounded to the nearest millisecond.
Times before then are invalid.
Examples:
```go
encode(time.Time("Jan 1 00:00:00 UTC 1970")) == [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]
encode(time.Time("Jan 1 00:00:01 UTC 1970")) == [0x00, 0x00, 0x00, 0x00, 0x3B, 0x9A, 0xCA, 0x00] // 1,000,000,000 ns
encode(time.Time("Mon Jan 2 15:04:05 -0700 MST 2006")) == [0x0F, 0xC4, 0xBB, 0xC1, 0x53, 0x03, 0x12, 0x00]
```
### Structs
An encoded struct is the concatenation of the encoding of its elements.
There is no length-prefix.
Examples:
```go
type MyStruct struct{
A int
B string
C time.Time
}
encode(MyStruct{4, "hello", time.Time("Mon Jan 2 15:04:05 -0700 MST 2006")}) ==
[0x01, 0x04, 0x01, 0x05, 0x68, 0x65, 0x6C, 0x6C, 0x6F, 0x0F, 0xC4, 0xBB, 0xC1, 0x53, 0x03, 0x12, 0x00]
```
## Merkle Trees
Simple Merkle trees are used in numerous places in Tendermint to compute a cryptographic digest of a data structure.
RIPEMD160 is always used as the hashing function.
The function `SimpleMerkleRoot` is a simple recursive function defined as follows:
```go
func SimpleMerkleRoot(hashes [][]byte) []byte{
switch len(hashes) {
case 0:
return nil
case 1:
return hashes[0]
default:
left := SimpleMerkleRoot(hashes[:(len(hashes)+1)/2])
right := SimpleMerkleRoot(hashes[(len(hashes)+1)/2:])
return RIPEMD160(append(left, right))
}
}
```
Note: we abuse notion and call `SimpleMerkleRoot` with arguments of type `struct` or type `[]struct`.
For `struct` arguments, we compute a `[][]byte` by sorting elements of the `struct` according to
field name and then hashing them.
For `[]struct` arguments, we compute a `[][]byte` by hashing the individual `struct` elements.
## JSON (TMJSON)
Signed messages (eg. votes, proposals) in the consensus are encoded in TMJSON, rather than TMBIN.
TMJSON is JSON where `[]byte` are encoded as uppercase hex, rather than base64.
When signing, the elements of a message are sorted by key and the sorted message is embedded in an
outer JSON that includes a `chain_id` field.
We call this encoding the CanonicalSignBytes. For instance, CanonicalSignBytes for a vote would look
like:
```json
{"chain_id":"my-chain-id","vote":{"block_id":{"hash":DEADBEEF,"parts":{"hash":BEEFDEAD,"total":3}},"height":3,"round":2,"timestamp":1234567890, "type":2}
```
Note how the fields within each level are sorted.
## Other
### MakeParts
Encode an object using TMBIN and slice it into parts.
```go
MakeParts(object, partSize)
```
### Part
```go
type Part struct {
Index int
Bytes byte[]
Proof byte[]
}
```

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docs/spec/consensus/abci.md View File

@ -1,192 +1 @@
# Application Blockchain Interface (ABCI)
ABCI is the interface between Tendermint (a state-machine replication engine)
and an application (the actual state machine).
The ABCI message types are defined in a [protobuf
file](https://github.com/tendermint/abci/blob/master/types/types.proto).
For full details on the ABCI message types and protocol, see the [ABCI
specificaiton](https://github.com/tendermint/abci/blob/master/specification.rst).
Be sure to read the specification if you're trying to build an ABCI app!
For additional details on server implementation, see the [ABCI
readme](https://github.com/tendermint/abci#implementation).
Here we provide some more details around the use of ABCI by Tendermint and
clarify common "gotchas".
## ABCI connections
Tendermint opens 3 ABCI connections to the app: one for Consensus, one for
Mempool, one for Queries.
## Async vs Sync
The main ABCI server (ie. non-GRPC) provides ordered asynchronous messages.
This is useful for DeliverTx and CheckTx, since it allows Tendermint to forward
transactions to the app before it's finished processing previous ones.
Thus, DeliverTx and CheckTx messages are sent asycnhronously, while all other
messages are sent synchronously.
## CheckTx and Commit
It is typical to hold three distinct states in an ABCI app: CheckTxState, DeliverTxState,
QueryState. The QueryState contains the latest committed state for a block.
The CheckTxState and DeliverTxState may be updated concurrently with one another.
Before Commit is called, Tendermint locks and flushes the mempool so that no new changes will happen
to CheckTxState. When Commit completes, it unlocks the mempool.
Thus, during Commit, it is safe to reset the QueryState and the CheckTxState to the latest DeliverTxState
(ie. the new state from executing all the txs in the block).
Note, however, that it is not possible to send transactions to Tendermint during Commit - if your app
tries to send a `/broadcast_tx` to Tendermint during Commit, it will deadlock.
## EndBlock Validator Updates
Updates to the Tendermint validator set can be made by returning `Validator`
objects in the `ResponseBeginBlock`:
```
message Validator {
bytes address = 1;
PubKey pub_key = 2;
int64 power = 3;
}
message PubKey {
string type = 1;
bytes data = 2;
}
```
The `pub_key` currently supports two types:
- `type = "ed25519" and `data = <raw 32-byte public key>`
- `type = "secp256k1" and `data = <33-byte OpenSSL compressed public key>`
If the address is provided, it must match the address of the pubkey, as
specified [here](/docs/spec/blockchain/encoding.md#Addresses)
(Note: In the v0.19 series, the `pub_key` is the [Amino encoded public
key](/docs/spec/blockchain/encoding.md#public-key-cryptography).
For Ed25519 pubkeys, the Amino prefix is always "1624DE6220". For example, the 32-byte Ed25519 pubkey
`76852933A4686A721442E931A8415F62F5F1AEDF4910F1F252FB393F74C40C85` would be
Amino encoded as
`1624DE622076852933A4686A721442E931A8415F62F5F1AEDF4910F1F252FB393F74C40C85`)
(Note: In old versions of Tendermint (pre-v0.19.0), the pubkey is just prefixed with a
single type byte, so for ED25519 we'd have `pub_key = 0x1 | pub`)
The `power` is the new voting power for the validator, with the
following rules:
- power must be non-negative
- if power is 0, the validator must already exist, and will be removed from the
validator set
- if power is non-0:
- if the validator does not already exist, it will be added to the validator
set with the given power
- if the validator does already exist, its power will be adjusted to the given power
## InitChain Validator Updates
ResponseInitChain has the option to return a list of validators.
If the list is not empty, Tendermint will adopt it for the validator set.
This way the application can determine the initial validator set for the
blockchain.
Note that if addressses are included in the returned validators, they must match
the address of the public key.
ResponseInitChain also includes ConsensusParams, but these are presently
ignored.
## Query
Query is a generic message type with lots of flexibility to enable diverse sets
of queries from applications. Tendermint has no requirements from the Query
message for normal operation - that is, the ABCI app developer need not implement Query functionality if they do not wish too.
That said, Tendermint makes a number of queries to support some optional
features. These are:
### Peer Filtering
When Tendermint connects to a peer, it sends two queries to the ABCI application
using the following paths, with no additional data:
- `/p2p/filter/addr/<IP:PORT>`, where `<IP:PORT>` denote the IP address and
the port of the connection
- `p2p/filter/id/<ID>`, where `<ID>` is the peer node ID (ie. the
pubkey.Address() for the peer's PubKey)
If either of these queries return a non-zero ABCI code, Tendermint will refuse
to connect to the peer.
## Info and the Handshake/Replay
On startup, Tendermint calls Info on the Query connection to get the latest
committed state of the app. The app MUST return information consistent with the
last block it succesfully completed Commit for.
If the app succesfully committed block H but not H+1, then `last_block_height =
H` and `last_block_app_hash = <hash returned by Commit for block H>`. If the app
failed during the Commit of block H, then `last_block_height = H-1` and
`last_block_app_hash = <hash returned by Commit for block H-1, which is the hash
in the header of block H>`.
We now distinguish three heights, and describe how Tendermint syncs itself with
the app.
```
storeBlockHeight = height of the last block Tendermint saw a commit for
stateBlockHeight = height of the last block for which Tendermint completed all
block processing and saved all ABCI results to disk
appBlockHeight = height of the last block for which ABCI app succesfully
completely Commit
```
Note we always have `storeBlockHeight >= stateBlockHeight` and `storeBlockHeight >= appBlockHeight`
Note also we never call Commit on an ABCI app twice for the same height.
The procedure is as follows.
First, some simeple start conditions:
If `appBlockHeight == 0`, then call InitChain.
If `storeBlockHeight == 0`, we're done.
Now, some sanity checks:
If `storeBlockHeight < appBlockHeight`, error
If `storeBlockHeight < stateBlockHeight`, panic
If `storeBlockHeight > stateBlockHeight+1`, panic
Now, the meat:
If `storeBlockHeight == stateBlockHeight && appBlockHeight < storeBlockHeight`,
replay all blocks in full from `appBlockHeight` to `storeBlockHeight`.
This happens if we completed processing the block, but the app forgot its height.
If `storeBlockHeight == stateBlockHeight && appBlockHeight == storeBlockHeight`, we're done
This happens if we crashed at an opportune spot.
If `storeBlockHeight == stateBlockHeight+1`
This happens if we started processing the block but didn't finish.
If `appBlockHeight < stateBlockHeight`
replay all blocks in full from `appBlockHeight` to `storeBlockHeight-1`,
and replay the block at `storeBlockHeight` using the WAL.
This happens if the app forgot the last block it committed.
If `appBlockHeight == stateBlockHeight`,
replay the last block (storeBlockHeight) in full.
This happens if we crashed before the app finished Commit
If appBlockHeight == storeBlockHeight {
update the state using the saved ABCI responses but dont run the block against the real app.
This happens if we crashed after the app finished Commit but before Tendermint saved the state.
[Moved](/docs/spec/software/abci.md)

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docs/spec/consensus/consensus.md View File

@ -0,0 +1,9 @@
We are working to finalize an updated Tendermint specification with formal
proofs of safety and liveness.
In the meantime, see the [description in the
docs](http://tendermint.readthedocs.io/en/master/specification/byzantine-consensus-algorithm.html).
There are also relevant but somewhat outdated descriptions in Jae Kwon's [original
whitepaper](https://tendermint.com/static/docs/tendermint.pdf) and Ethan Buchman's [master's
thesis](https://atrium.lib.uoguelph.ca/xmlui/handle/10214/9769).

docs/spec/blockchain/light-client.md → docs/spec/consensus/light-client.md View File


+ 1
- 33
docs/spec/consensus/wal.md View File

@ -1,33 +1 @@
# WAL
Consensus module writes every message to the WAL (write-ahead log).
It also issues fsync syscall through
[File#Sync](https://golang.org/pkg/os/#File.Sync) for messages signed by this
node (to prevent double signing).
Under the hood, it uses
[autofile.Group](https://godoc.org/github.com/tendermint/tmlibs/autofile#Group),
which rotates files when those get too big (> 10MB).
The total maximum size is 1GB. We only need the latest block and the block before it,
but if the former is dragging on across many rounds, we want all those rounds.
## Replay
Consensus module will replay all the messages of the last height written to WAL
before a crash (if such occurs).
The private validator may try to sign messages during replay because it runs
somewhat autonomously and does not know about replay process.
For example, if we got all the way to precommit in the WAL and then crash,
after we replay the proposal message, the private validator will try to sign a
prevote. But it will fail. That's ok because we’ll see the prevote later in the
WAL. Then it will go to precommit, and that time it will work because the
private validator contains the `LastSignBytes` and then we’ll replay the
precommit from the WAL.
Make sure to read about [WAL
corruption](https://tendermint.readthedocs.io/projects/tools/en/master/specification/corruption.html#wal-corruption)
and recovery strategies.
[Moved](/docs/spec/software/wal.md)

+ 192
- 0
docs/spec/software/abci.md View File

@ -0,0 +1,192 @@
# Application Blockchain Interface (ABCI)
ABCI is the interface between Tendermint (a state-machine replication engine)
and an application (the actual state machine).
The ABCI message types are defined in a [protobuf
file](https://github.com/tendermint/abci/blob/master/types/types.proto).
For full details on the ABCI message types and protocol, see the [ABCI
specificaiton](https://github.com/tendermint/abci/blob/master/specification.rst).
Be sure to read the specification if you're trying to build an ABCI app!
For additional details on server implementation, see the [ABCI
readme](https://github.com/tendermint/abci#implementation).
Here we provide some more details around the use of ABCI by Tendermint and
clarify common "gotchas".
## ABCI connections
Tendermint opens 3 ABCI connections to the app: one for Consensus, one for
Mempool, one for Queries.
## Async vs Sync
The main ABCI server (ie. non-GRPC) provides ordered asynchronous messages.
This is useful for DeliverTx and CheckTx, since it allows Tendermint to forward
transactions to the app before it's finished processing previous ones.
Thus, DeliverTx and CheckTx messages are sent asycnhronously, while all other
messages are sent synchronously.
## CheckTx and Commit
It is typical to hold three distinct states in an ABCI app: CheckTxState, DeliverTxState,
QueryState. The QueryState contains the latest committed state for a block.
The CheckTxState and DeliverTxState may be updated concurrently with one another.
Before Commit is called, Tendermint locks and flushes the mempool so that no new changes will happen
to CheckTxState. When Commit completes, it unlocks the mempool.
Thus, during Commit, it is safe to reset the QueryState and the CheckTxState to the latest DeliverTxState
(ie. the new state from executing all the txs in the block).
Note, however, that it is not possible to send transactions to Tendermint during Commit - if your app
tries to send a `/broadcast_tx` to Tendermint during Commit, it will deadlock.
## EndBlock Validator Updates
Updates to the Tendermint validator set can be made by returning `Validator`
objects in the `ResponseBeginBlock`:
```
message Validator {
bytes address = 1;
PubKey pub_key = 2;
int64 power = 3;
}
message PubKey {
string type = 1;
bytes data = 2;
}
```
The `pub_key` currently supports two types:
- `type = "ed25519" and `data = <raw 32-byte public key>`
- `type = "secp256k1" and `data = <33-byte OpenSSL compressed public key>`
If the address is provided, it must match the address of the pubkey, as
specified [here](/docs/spec/blockchain/encoding.md#Addresses)
(Note: In the v0.19 series, the `pub_key` is the [Amino encoded public
key](/docs/spec/blockchain/encoding.md#public-key-cryptography).
For Ed25519 pubkeys, the Amino prefix is always "1624DE6220". For example, the 32-byte Ed25519 pubkey
`76852933A4686A721442E931A8415F62F5F1AEDF4910F1F252FB393F74C40C85` would be
Amino encoded as
`1624DE622076852933A4686A721442E931A8415F62F5F1AEDF4910F1F252FB393F74C40C85`)
(Note: In old versions of Tendermint (pre-v0.19.0), the pubkey is just prefixed with a
single type byte, so for ED25519 we'd have `pub_key = 0x1 | pub`)
The `power` is the new voting power for the validator, with the
following rules:
- power must be non-negative
- if power is 0, the validator must already exist, and will be removed from the
validator set
- if power is non-0:
- if the validator does not already exist, it will be added to the validator
set with the given power
- if the validator does already exist, its power will be adjusted to the given power
## InitChain Validator Updates
ResponseInitChain has the option to return a list of validators.
If the list is not empty, Tendermint will adopt it for the validator set.
This way the application can determine the initial validator set for the
blockchain.
Note that if addressses are included in the returned validators, they must match
the address of the public key.
ResponseInitChain also includes ConsensusParams, but these are presently
ignored.
## Query
Query is a generic message type with lots of flexibility to enable diverse sets
of queries from applications. Tendermint has no requirements from the Query
message for normal operation - that is, the ABCI app developer need not implement Query functionality if they do not wish too.
That said, Tendermint makes a number of queries to support some optional
features. These are:
### Peer Filtering
When Tendermint connects to a peer, it sends two queries to the ABCI application
using the following paths, with no additional data:
- `/p2p/filter/addr/<IP:PORT>`, where `<IP:PORT>` denote the IP address and
the port of the connection
- `p2p/filter/id/<ID>`, where `<ID>` is the peer node ID (ie. the
pubkey.Address() for the peer's PubKey)
If either of these queries return a non-zero ABCI code, Tendermint will refuse
to connect to the peer.
## Info and the Handshake/Replay
On startup, Tendermint calls Info on the Query connection to get the latest
committed state of the app. The app MUST return information consistent with the
last block it succesfully completed Commit for.
If the app succesfully committed block H but not H+1, then `last_block_height =
H` and `last_block_app_hash = <hash returned by Commit for block H>`. If the app
failed during the Commit of block H, then `last_block_height = H-1` and
`last_block_app_hash = <hash returned by Commit for block H-1, which is the hash
in the header of block H>`.
We now distinguish three heights, and describe how Tendermint syncs itself with
the app.
```
storeBlockHeight = height of the last block Tendermint saw a commit for
stateBlockHeight = height of the last block for which Tendermint completed all
block processing and saved all ABCI results to disk
appBlockHeight = height of the last block for which ABCI app succesfully
completely Commit
```
Note we always have `storeBlockHeight >= stateBlockHeight` and `storeBlockHeight >= appBlockHeight`
Note also we never call Commit on an ABCI app twice for the same height.
The procedure is as follows.
First, some simeple start conditions:
If `appBlockHeight == 0`, then call InitChain.
If `storeBlockHeight == 0`, we're done.
Now, some sanity checks:
If `storeBlockHeight < appBlockHeight`, error
If `storeBlockHeight < stateBlockHeight`, panic
If `storeBlockHeight > stateBlockHeight+1`, panic
Now, the meat:
If `storeBlockHeight == stateBlockHeight && appBlockHeight < storeBlockHeight`,
replay all blocks in full from `appBlockHeight` to `storeBlockHeight`.
This happens if we completed processing the block, but the app forgot its height.
If `storeBlockHeight == stateBlockHeight && appBlockHeight == storeBlockHeight`, we're done
This happens if we crashed at an opportune spot.
If `storeBlockHeight == stateBlockHeight+1`
This happens if we started processing the block but didn't finish.
If `appBlockHeight < stateBlockHeight`
replay all blocks in full from `appBlockHeight` to `storeBlockHeight-1`,
and replay the block at `storeBlockHeight` using the WAL.
This happens if the app forgot the last block it committed.
If `appBlockHeight == stateBlockHeight`,
replay the last block (storeBlockHeight) in full.
This happens if we crashed before the app finished Commit
If appBlockHeight == storeBlockHeight {
update the state using the saved ABCI responses but dont run the block against the real app.
This happens if we crashed after the app finished Commit but before Tendermint saved the state.

+ 33
- 0
docs/spec/software/wal.md View File

@ -0,0 +1,33 @@
# WAL
Consensus module writes every message to the WAL (write-ahead log).
It also issues fsync syscall through
[File#Sync](https://golang.org/pkg/os/#File.Sync) for messages signed by this
node (to prevent double signing).
Under the hood, it uses
[autofile.Group](https://godoc.org/github.com/tendermint/tmlibs/autofile#Group),
which rotates files when those get too big (> 10MB).
The total maximum size is 1GB. We only need the latest block and the block before it,
but if the former is dragging on across many rounds, we want all those rounds.
## Replay
Consensus module will replay all the messages of the last height written to WAL
before a crash (if such occurs).
The private validator may try to sign messages during replay because it runs
somewhat autonomously and does not know about replay process.
For example, if we got all the way to precommit in the WAL and then crash,
after we replay the proposal message, the private validator will try to sign a
prevote. But it will fail. That's ok because we’ll see the prevote later in the
WAL. Then it will go to precommit, and that time it will work because the
private validator contains the `LastSignBytes` and then we’ll replay the
precommit from the WAL.
Make sure to read about [WAL
corruption](https://tendermint.readthedocs.io/projects/tools/en/master/specification/corruption.html#wal-corruption)
and recovery strategies.

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