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piece_reader.go
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piece_reader.go
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package sealer
import (
"bufio"
"context"
"io"
"sync"
lru "github.com/hashicorp/golang-lru/v2"
"github.com/ipfs/go-cid"
"go.opencensus.io/stats"
"go.opencensus.io/tag"
"golang.org/x/xerrors"
"github.com/filecoin-project/go-state-types/abi"
"github.com/filecoin-project/lotus/metrics"
)
// For small read skips, it's faster to "burn" some bytes than to setup new sector reader.
// Assuming 1ms stream seek latency, and 1G/s stream rate, we're willing to discard up to 1 MiB.
var MaxPieceReaderBurnBytes int64 = 1 << 20 // 1M
var ReadBuf = 128 * (127 * 8) // unpadded(128k)
var MinRandomReadSize = int64(4 << 10)
type pieceGetter func(offset, size uint64) (io.ReadCloser, error)
type pieceReader struct {
getReader pieceGetter
pieceCid cid.Cid
len abi.UnpaddedPieceSize
onClose context.CancelFunc
seqMCtx context.Context
atMCtx context.Context
closed bool
seqAt int64 // next byte to be read by io.Reader
// sequential reader
seqMu sync.Mutex
r io.ReadCloser
br *bufio.Reader
rAt int64
// random read cache
remReads *lru.Cache[int64, []byte] // data start offset -> data
// todo try carrying a "bytes read sequentially so far" counter with those
// cacahed byte buffers, increase buffer sizes when we see that we're doing
// a long sequential read
}
func (p *pieceReader) init(ctx context.Context) (_ *pieceReader, err error) {
stats.Record(ctx, metrics.DagStorePRInitCount.M(1))
p.seqMCtx, _ = tag.New(ctx, tag.Upsert(metrics.PRReadType, "seq"))
p.atMCtx, _ = tag.New(ctx, tag.Upsert(metrics.PRReadType, "rand"))
p.remReads, err = lru.New[int64, []byte](100)
if err != nil {
return nil, err
}
p.rAt = 0
p.r, err = p.getReader(uint64(p.rAt), uint64(p.len))
if err != nil {
return nil, err
}
if p.r == nil {
return nil, nil
}
p.br = bufio.NewReaderSize(p.r, ReadBuf)
return p, nil
}
func (p *pieceReader) check() error {
if p.closed {
return xerrors.Errorf("reader closed")
}
return nil
}
func (p *pieceReader) Close() error {
p.seqMu.Lock()
defer p.seqMu.Unlock()
if err := p.check(); err != nil {
return err
}
if p.r != nil {
if err := p.r.Close(); err != nil {
return err
}
p.r = nil
}
p.onClose()
p.closed = true
return nil
}
func (p *pieceReader) Read(b []byte) (int, error) {
p.seqMu.Lock()
defer p.seqMu.Unlock()
if err := p.check(); err != nil {
return 0, err
}
n, err := p.readSeqReader(b)
p.seqAt += int64(n)
return n, err
}
func (p *pieceReader) Seek(offset int64, whence int) (int64, error) {
p.seqMu.Lock()
defer p.seqMu.Unlock()
if err := p.check(); err != nil {
return 0, err
}
switch whence {
case io.SeekStart:
p.seqAt = offset
case io.SeekCurrent:
p.seqAt += offset
case io.SeekEnd:
p.seqAt = int64(p.len) + offset
default:
return 0, xerrors.Errorf("bad whence")
}
return p.seqAt, nil
}
func (p *pieceReader) readSeqReader(b []byte) (n int, err error) {
off := p.seqAt
if err := p.check(); err != nil {
return 0, err
}
stats.Record(p.seqMCtx, metrics.DagStorePRBytesRequested.M(int64(len(b))))
// 1. Get the backing reader into the correct position
// if the backing reader is ahead of the offset we want, or more than
// MaxPieceReaderBurnBytes behind, reset the reader
if p.r == nil || p.rAt > off || p.rAt+MaxPieceReaderBurnBytes < off {
if p.r != nil {
if err := p.r.Close(); err != nil {
return 0, xerrors.Errorf("closing backing reader: %w", err)
}
p.r = nil
p.br = nil
}
log.Debugw("pieceReader new stream", "piece", p.pieceCid, "at", p.rAt, "off", off-p.rAt, "n", len(b))
if off > p.rAt {
stats.Record(p.seqMCtx, metrics.DagStorePRSeekForwardBytes.M(off-p.rAt), metrics.DagStorePRSeekForwardCount.M(1))
} else {
stats.Record(p.seqMCtx, metrics.DagStorePRSeekBackBytes.M(p.rAt-off), metrics.DagStorePRSeekBackCount.M(1))
}
p.rAt = off
p.r, err = p.getReader(uint64(p.rAt), uint64(p.len))
p.br = bufio.NewReaderSize(p.r, ReadBuf)
if err != nil {
return 0, xerrors.Errorf("getting backing reader: %w", err)
}
}
// 2. Check if we need to burn some bytes
if off > p.rAt {
stats.Record(p.seqMCtx, metrics.DagStorePRBytesDiscarded.M(off-p.rAt), metrics.DagStorePRDiscardCount.M(1))
n, err := io.CopyN(io.Discard, p.br, off-p.rAt)
p.rAt += n
if err != nil {
return 0, xerrors.Errorf("discarding read gap: %w", err)
}
}
// 3. Sanity check
if off != p.rAt {
return 0, xerrors.Errorf("bad reader offset; requested %d; at %d", off, p.rAt)
}
// 4. Read!
n, err = io.ReadFull(p.br, b)
if n < len(b) {
log.Debugw("pieceReader short read", "piece", p.pieceCid, "at", p.rAt, "toEnd", int64(p.len)-p.rAt, "n", len(b), "read", n, "err", err)
}
if err == io.ErrUnexpectedEOF {
err = io.EOF
}
p.rAt += int64(n)
return n, err
}
func (p *pieceReader) ReadAt(b []byte, off int64) (n int, err error) {
stats.Record(p.atMCtx, metrics.DagStorePRBytesRequested.M(int64(len(b))))
var filled int64
// try to get a buf from lru
data, ok := p.remReads.Get(off)
if ok {
n = copy(b, data)
filled += int64(n)
if n < len(data) {
p.remReads.Add(off+int64(n), data[n:])
// keep the header buffered
if off != 0 {
p.remReads.Remove(off)
}
}
stats.Record(p.atMCtx, metrics.DagStorePRAtHitBytes.M(int64(n)), metrics.DagStorePRAtHitCount.M(1))
// dagstore/pr_at_hit_bytes, dagstore/pr_at_hit_count
}
if filled == int64(len(b)) {
// dagstore/pr_at_cache_fill_count
stats.Record(p.atMCtx, metrics.DagStorePRAtCacheFillCount.M(1))
return n, nil
}
readOff := off + filled
readSize := int64(len(b)) - filled
smallRead := readSize < MinRandomReadSize
if smallRead {
// read into small read buf
readBuf := make([]byte, MinRandomReadSize)
bn, err := p.readInto(readBuf, readOff)
if err != nil && err != io.EOF {
return int(filled), err
}
_ = stats.RecordWithTags(p.atMCtx, []tag.Mutator{tag.Insert(metrics.PRReadSize, "small")}, metrics.DagStorePRAtReadBytes.M(int64(bn)), metrics.DagStorePRAtReadCount.M(1))
// reslice so that the slice is the data
readBuf = readBuf[:bn]
// fill user data
used := copy(b[filled:], readBuf[:])
filled += int64(used)
readBuf = readBuf[used:]
// cache the rest
if len(readBuf) > 0 {
p.remReads.Add(readOff+int64(used), readBuf)
}
} else {
// read into user buf
bn, err := p.readInto(b[filled:], readOff)
if err != nil {
return int(filled), err
}
filled += int64(bn)
_ = stats.RecordWithTags(p.atMCtx, []tag.Mutator{tag.Insert(metrics.PRReadSize, "big")}, metrics.DagStorePRAtReadBytes.M(int64(bn)), metrics.DagStorePRAtReadCount.M(1))
}
if filled < int64(len(b)) {
return int(filled), io.EOF
}
return int(filled), nil
}
func (p *pieceReader) readInto(b []byte, off int64) (n int, err error) {
rd, err := p.getReader(uint64(off), uint64(len(b)))
if err != nil {
return 0, xerrors.Errorf("getting reader: %w", err)
}
n, err = io.ReadFull(rd, b)
cerr := rd.Close()
if err == io.ErrUnexpectedEOF {
err = io.EOF
}
if err != nil {
return n, err
}
return n, cerr
}