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core.go
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core.go
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package chainsync
import (
"fmt"
"sort"
"sync"
"time"
"github.com/rs/zerolog"
"github.com/onflow/flow-go/model/chainsync"
"github.com/onflow/flow-go/model/flow"
"github.com/onflow/flow-go/module"
)
const (
// DefaultPollNodes is the default number of nodes we send a message to on
// each poll interval.
DefaultPollNodes uint = 3
// DefaultBlockRequestNodes is the default number of nodes we request a
// block resource from.
DefaultBlockRequestNodes uint = 3
// DefaultQueuedHeightMultiplicity limits the number of heights we queue
// above the current finalized height.
DefaultQueuedHeightMultiplicity uint = 4
)
type Config struct {
RetryInterval time.Duration // the initial interval before we retry a request, uses exponential backoff
Tolerance uint // determines how big of a difference in block heights we tolerated before actively syncing with range requests
MaxAttempts uint // the maximum number of attempts we make for each requested block/height before discarding
MaxSize uint // the maximum number of blocks we request in the same block request message
MaxRequests uint // the maximum number of requests we send during each scanning period
}
func DefaultConfig() Config {
return Config{
RetryInterval: 4 * time.Second,
Tolerance: 10,
MaxAttempts: 5,
MaxSize: 64,
MaxRequests: 3,
}
}
// Core contains core logic, configuration, and state for chain state
// synchronization. It is generic to chain type, so it works for both consensus
// and collection nodes.
//
// Core should be wrapped by a type-aware engine that manages the specifics of
// each chain. Example: https://github.com/onflow/flow-go/blob/master/engine/common/synchronization/engine.go
//
// Core is safe for concurrent use by multiple goroutines.
type Core struct {
log zerolog.Logger
Config Config
mu sync.Mutex
heights map[uint64]*chainsync.Status
blockIDs map[flow.Identifier]*chainsync.Status
metrics module.ChainSyncMetrics
localFinalizedHeight uint64
}
func New(log zerolog.Logger, config Config, metrics module.ChainSyncMetrics, chainID flow.ChainID) (*Core, error) {
core := &Core{
log: log.With().Str("sync_core", chainID.String()).Logger(),
Config: config,
heights: make(map[uint64]*chainsync.Status),
blockIDs: make(map[flow.Identifier]*chainsync.Status),
metrics: metrics,
localFinalizedHeight: 0,
}
return core, nil
}
// HandleBlock handles receiving a new block from another node. It returns
// true if the block should be processed by the compliance layer and false
// if it should be ignored.
func (c *Core) HandleBlock(header *flow.Header) bool {
log := c.log
if c.log.Debug().Enabled() {
log = c.log.With().Str("block_id", header.ID().String()).Uint64("block_height", header.Height).Logger()
}
c.mu.Lock()
defer c.mu.Unlock()
status := c.getRequestStatus(header.Height, header.ID())
// if we never asked for this block, discard it
if !status.WasQueued() {
log.Debug().Msg("discarding not queued block")
return false
}
// if we have already received this block, exit
if status.WasReceived() {
log.Debug().Msg("discarding not received block")
return false
}
// this is a new block, remember that we've seen it
status.Header = header
status.Received = time.Now()
// track it by ID and by height so we don't accidentally request it again
c.blockIDs[header.ID()] = status
c.heights[header.Height] = status
log.Debug().Msg("handled block")
return true
}
// HandleHeight handles receiving a new highest finalized height from another node.
// If the height difference between local and the reported height is outside tolerance, we do nothing.
// Otherwise, we queue each missing height.
func (c *Core) HandleHeight(final *flow.Header, height uint64) {
log := c.log.With().Uint64("final_height", final.Height).Uint64("recv_height", height).Logger()
log.Debug().Msg("received height")
// don't bother queueing anything if we're within tolerance
if c.WithinTolerance(final, height) {
log.Debug().Msg("height within tolerance - discarding")
return
}
// if we are sufficiently behind, we want to sync the missing blocks
if height > final.Height {
c.mu.Lock()
defer c.mu.Unlock()
// limit to request up to DefaultQueuedHeightMultiplicity*MaxRequests*MaxSize blocks from the peer.
// without this limit, then if we are falling far behind,
// we would queue up too many heights.
heightLimit := final.Height + uint64(DefaultQueuedHeightMultiplicity*c.Config.MaxRequests*c.Config.MaxSize)
if height > heightLimit {
height = heightLimit
}
for h := final.Height + 1; h <= height; h++ {
c.requeueHeight(h)
}
log.Debug().Msgf("requeued heights [%d-%d]", final.Height+1, height)
}
}
func (c *Core) RequestBlock(blockID flow.Identifier, height uint64) {
log := c.log.With().Str("block_id", blockID.String()).Uint64("height", height).Logger()
// requesting a block by its ID storing the height to prune more efficiently
c.mu.Lock()
defer c.mu.Unlock()
// if we already received this block, reset the status so we can re-queue
status := c.blockIDs[blockID]
if status.WasReceived() {
log.Debug().Msgf("requested block was already received")
delete(c.blockIDs, status.Header.ID())
delete(c.heights, status.Header.Height)
}
c.queueByBlockID(blockID, height)
log.Debug().Msgf("enqueued requested block")
}
func (c *Core) RequestHeight(height uint64) {
c.mu.Lock()
defer c.mu.Unlock()
c.requeueHeight(height)
c.log.Debug().Uint64("height", height).Msg("enqueued requested height")
}
// requeueHeight queues the given height, ignoring any previously received
// blocks at that height
func (c *Core) requeueHeight(height uint64) {
// if we already received this block, reset the status so we can re-queue
status := c.heights[height]
if status.WasReceived() {
delete(c.blockIDs, status.Header.ID())
delete(c.heights, status.Header.Height)
}
c.queueByHeight(height)
}
// ScanPending scans all pending block statuses for blocks that should be
// requested. It apportions requestable items into range and batch requests
// according to configured maximums, giving precedence to range requests.
func (c *Core) ScanPending(final *flow.Header) ([]chainsync.Range, []chainsync.Batch) {
c.mu.Lock()
defer c.mu.Unlock()
log := c.log.With().Uint64("final_height", final.Height).Logger()
// prune if the current height is less than the new height
c.prune(final)
// get all items that are eligible for initial or re-requesting
heights, blockIDs := c.getRequestableItems()
c.log.Debug().Msgf("scan found %d requestable heights, %d requestable block IDs", len(heights), len(blockIDs))
// convert to valid range and batch requests
ranges := c.getRanges(heights)
batches := c.getBatches(blockIDs)
log.Debug().Str("ranges", fmt.Sprintf("%v", ranges)).Str("batches", fmt.Sprintf("%v", batches)).Msg("compiled range and batch requests")
return c.selectRequests(ranges, batches)
}
// WithinTolerance returns whether or not the given height is within configured
// height tolerance, wrt the given local finalized header.
func (c *Core) WithinTolerance(final *flow.Header, height uint64) bool {
lower := final.Height - uint64(c.Config.Tolerance)
if lower > final.Height { // underflow check
lower = 0
}
upper := final.Height + uint64(c.Config.Tolerance)
return height >= lower && height <= upper
}
// queueByHeight queues a request for the finalized block at the given height,
// only if no equivalent request has been queued before.
func (c *Core) queueByHeight(height uint64) {
// do not queue the block if the height is lower or the same as the local finalized height
// the check != 0 is necessary or we will never queue blocks at height 0
if height <= c.localFinalizedHeight && c.localFinalizedHeight != 0 {
return
}
// only queue the request if have never queued it before
if c.heights[height].WasQueued() {
return
}
// queue the request
c.heights[height] = chainsync.NewQueuedStatus(height)
}
// queueByBlockID queues a request for a block by block ID, only if no
// equivalent request has been queued before.
func (c *Core) queueByBlockID(blockID flow.Identifier, height uint64) {
// do not queue the block if the height is lower or the same as the local finalized height
// the check != 0 is necessary or we will never queue blocks at height 0
if height <= c.localFinalizedHeight && c.localFinalizedHeight != 0 {
return
}
// only queue the request if have never queued it before
if c.blockIDs[blockID].WasQueued() {
return
}
// queue the request
c.blockIDs[blockID] = chainsync.NewQueuedStatus(height)
}
// getRequestStatus retrieves a request status for a block, regardless of
// whether it was queued by height or by block ID.
func (c *Core) getRequestStatus(height uint64, blockID flow.Identifier) *chainsync.Status {
heightStatus := c.heights[height]
idStatus := c.blockIDs[blockID]
if idStatus.WasQueued() {
return idStatus
}
// Only return the height status if there is no matching status for the ID
if heightStatus.WasQueued() {
return heightStatus
}
return nil
}
// prune removes any pending requests which we have received and which is below
// the finalized height, or which we received sufficiently long ago.
func (c *Core) prune(final *flow.Header) {
if c.localFinalizedHeight >= final.Height {
return
}
c.localFinalizedHeight = final.Height
// track how many statuses we are pruning
initialHeights := len(c.heights)
initialBlockIDs := len(c.blockIDs)
for height, status := range c.heights {
if height <= final.Height {
delete(c.heights, height)
c.metrics.PrunedBlockByHeight(status)
}
}
for blockID, status := range c.blockIDs {
if status.BlockHeight <= final.Height {
delete(c.blockIDs, blockID)
c.metrics.PrunedBlockById(status)
}
}
currentHeights := len(c.heights)
currentBlockIDs := len(c.blockIDs)
prunedHeights := initialHeights - currentHeights
prunedBlockIDs := initialBlockIDs - currentBlockIDs
c.metrics.PrunedBlocks(prunedHeights, prunedBlockIDs, currentHeights, currentBlockIDs)
c.log.Debug().
Uint64("final_height", final.Height).
Msgf("pruned %d heights, %d block IDs", prunedHeights, prunedBlockIDs)
}
func (c *Core) Prune(final *flow.Header) {
c.mu.Lock()
defer c.mu.Unlock()
c.prune(final)
}
// getRequestableItems will find all block IDs and heights that are eligible
// to be requested.
func (c *Core) getRequestableItems() ([]uint64, []flow.Identifier) {
// TODO: we will probably want to limit the maximum amount of in-flight
// requests and maximum amount of blocks requested at the same time here;
// for now, we just ignore that problem, but once we do, we should always
// prioritize range requests over batch requests
now := time.Now()
// create a list of all height requests that should be sent
var heights []uint64
for height, status := range c.heights {
// if the last request is young enough, skip
retryAfter := status.Requested.Add(c.Config.RetryInterval << status.Attempts)
if now.Before(retryAfter) {
continue
}
// if we've already received this block, skip
if status.WasReceived() {
continue
}
// if we reached maximum number of attempts, delete
if status.Attempts >= c.Config.MaxAttempts {
delete(c.heights, height)
continue
}
// otherwise, append to heights to be requested
heights = append(heights, height)
}
// create list of all the block IDs blocks that are missing
var blockIDs []flow.Identifier
for blockID, status := range c.blockIDs {
// if the last request is young enough, skip
retryAfter := status.Requested.Add(c.Config.RetryInterval << status.Attempts)
if now.Before(retryAfter) {
continue
}
// if we've already received this block, skip
if status.WasReceived() {
continue
}
// if we reached the maximum number of attempts for a queue item, drop
if status.Attempts >= c.Config.MaxAttempts {
delete(c.blockIDs, blockID)
continue
}
// otherwise, append to blockIDs to be requested
blockIDs = append(blockIDs, blockID)
}
return heights, blockIDs
}
// RangeRequested updates status state for a range of block heights that has
// been successfully requested. Must be called when a range request is submitted.
func (c *Core) RangeRequested(ran chainsync.Range) {
c.mu.Lock()
defer c.mu.Unlock()
c.metrics.RangeRequested(ran)
for height := ran.From; height <= ran.To; height++ {
status, exists := c.heights[height]
if !exists {
return
}
status.Requested = time.Now()
status.Attempts++
}
}
// BatchRequested updates status state for a batch of block IDs that has been
// successfully requested. Must be called when a batch request is submitted.
func (c *Core) BatchRequested(batch chainsync.Batch) {
c.mu.Lock()
defer c.mu.Unlock()
c.metrics.BatchRequested(batch)
for _, blockID := range batch.BlockIDs {
status, exists := c.blockIDs[blockID]
if !exists {
return
}
status.Requested = time.Now()
status.Attempts++
}
}
// getRanges returns a set of ranges of heights that can be used as range
// requests.
func (c *Core) getRanges(heights []uint64) []chainsync.Range {
// sort the heights so we can build contiguous ranges more easily
sort.Slice(heights, func(i int, j int) bool {
return heights[i] < heights[j]
})
// build contiguous height ranges with maximum batch size
start := uint64(0)
end := uint64(0)
var ranges []chainsync.Range
for index, height := range heights {
// on the first iteration, we set the start pointer, so we don't need to
// guard the for loop when heights is empty
if index == 0 {
start = height
}
// we always forward the end pointer to the new height
end = height
// if we have the end of the loop, we always create one final range
if index >= len(heights)-1 {
r := chainsync.Range{From: start, To: end}
ranges = append(ranges, r)
break
}
// at this point, we will have a next height as iteration will continue
nextHeight := heights[index+1]
// if we have reached the maximum size for a range, we create the range
// and forward the start pointer to the next height
rangeSize := end - start + 1
if rangeSize >= uint64(c.Config.MaxSize) {
r := chainsync.Range{From: start, To: end}
ranges = append(ranges, r)
start = nextHeight
continue
}
// if end is more than one smaller than the next height, we have a gap
// next, so we create a range and forward the start pointer
if nextHeight > end+1 {
r := chainsync.Range{From: start, To: end}
ranges = append(ranges, r)
start = nextHeight
continue
}
}
return ranges
}
// getBatches returns a set of batches that can be used in batch requests.
func (c *Core) getBatches(blockIDs []flow.Identifier) []chainsync.Batch {
var batches []chainsync.Batch
// split the block IDs into maximum sized requests
for from := 0; from < len(blockIDs); from += int(c.Config.MaxSize) {
// make sure last range is not out of bounds
to := from + int(c.Config.MaxSize)
if to > len(blockIDs) {
to = len(blockIDs)
}
// create the block IDs slice
requestIDs := blockIDs[from:to]
batch := chainsync.Batch{
BlockIDs: requestIDs,
}
batches = append(batches, batch)
}
return batches
}
// selectRequests selects which requests should be submitted, given a set of
// candidate range and batch requests. Range requests are given precedence and
// the total number of requests does not exceed the configured request maximum.
func (c *Core) selectRequests(ranges []chainsync.Range, batches []chainsync.Batch) ([]chainsync.Range, []chainsync.Batch) {
max := int(c.Config.MaxRequests)
if len(ranges) >= max {
return ranges[:max], nil
}
if len(ranges)+len(batches) >= max {
return ranges, batches[:max-len(ranges)]
}
return ranges, batches
}