Jeremy Tregunna
6fc3be617d
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Adds a complete LSM-based storage engine with these features: - Single-writer based architecture for the storage engine - WAL for durability, and hey it's configurable - MemTable with skip list implementation for fast read/writes - SSTable with block-based structure for on-disk level-based storage - Background compaction with tiered strategy - ACID transactions - Good documentation (I hope)
73 lines
1.8 KiB
Go
73 lines
1.8 KiB
Go
package block
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import (
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"encoding/binary"
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"fmt"
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"github.com/cespare/xxhash/v2"
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)
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// Reader provides methods to read data from a serialized block
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type Reader struct {
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data []byte
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restartPoints []uint32
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numRestarts uint32
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checksum uint64
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}
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// NewReader creates a new block reader
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func NewReader(data []byte) (*Reader, error) {
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if len(data) < BlockFooterSize {
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return nil, fmt.Errorf("block data too small: %d bytes", len(data))
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}
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// Read footer
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footerOffset := len(data) - BlockFooterSize
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numRestarts := binary.LittleEndian.Uint32(data[footerOffset : footerOffset+4])
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checksum := binary.LittleEndian.Uint64(data[footerOffset+4:])
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// Verify checksum - the checksum covers everything except the checksum itself
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computedChecksum := xxhash.Sum64(data[:len(data)-8])
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if computedChecksum != checksum {
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return nil, fmt.Errorf("block checksum mismatch: expected %d, got %d",
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checksum, computedChecksum)
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}
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// Read restart points
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restartOffset := footerOffset - int(numRestarts)*4
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if restartOffset < 0 {
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return nil, fmt.Errorf("invalid restart points offset")
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}
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restartPoints := make([]uint32, numRestarts)
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for i := uint32(0); i < numRestarts; i++ {
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restartPoints[i] = binary.LittleEndian.Uint32(
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data[restartOffset+int(i)*4:])
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}
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reader := &Reader{
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data: data,
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restartPoints: restartPoints,
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numRestarts: numRestarts,
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checksum: checksum,
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}
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return reader, nil
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}
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// Iterator returns an iterator for the block
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func (r *Reader) Iterator() *Iterator {
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// Calculate the data end position (everything before the restart points array)
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dataEnd := len(r.data) - BlockFooterSize - 4*len(r.restartPoints)
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return &Iterator{
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reader: r,
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currentPos: 0,
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currentKey: nil,
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currentVal: nil,
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restartIdx: 0,
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initialized: false,
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dataEnd: uint32(dataEnd),
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}
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}
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