From 00b1659ddedf99e70dbc25576acc662d1aa3032a Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Sat, 15 Aug 2020 14:44:29 +0300
Subject: [PATCH] lib: dump compressed block contents on error during
 decompression

This should improve detecting root cause for https://github.com/facebook/zstd/issues/2222
---
 lib/encoding/compress.go            | 8 +++++++-
 lib/encoding/encoding.go            | 4 ++--
 lib/mergeset/block_stream_reader.go | 2 +-
 lib/mergeset/metaindex_row.go       | 2 +-
 lib/mergeset/part_search.go         | 2 +-
 5 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/lib/encoding/compress.go b/lib/encoding/compress.go
index 4739b8962..b8acf541e 100644
--- a/lib/encoding/compress.go
+++ b/lib/encoding/compress.go
@@ -1,6 +1,8 @@
 package encoding
 
 import (
+	"fmt"
+
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding/zstd"
 	"github.com/VictoriaMetrics/metrics"
 )
@@ -22,7 +24,11 @@ func CompressZSTDLevel(dst, src []byte, compressLevel int) []byte {
 // the appended dst.
 func DecompressZSTD(dst, src []byte) ([]byte, error) {
 	decompressCalls.Inc()
-	return zstd.Decompress(dst, src)
+	b, err := zstd.Decompress(dst, src)
+	if err != nil {
+		return b, fmt.Errorf("cannot decompress zstd block with len=%d to a buffer with len=%d: %w; block data (hex): %X", len(src), len(dst), err, src)
+	}
+	return b, nil
 }
 
 var (
diff --git a/lib/encoding/encoding.go b/lib/encoding/encoding.go
index 807f8eb17..01829c815 100644
--- a/lib/encoding/encoding.go
+++ b/lib/encoding/encoding.go
@@ -166,7 +166,7 @@ func unmarshalInt64Array(dst []int64, src []byte, mt MarshalType, firstValue int
 		bb := bbPool.Get()
 		bb.B, err = DecompressZSTD(bb.B[:0], src)
 		if err != nil {
-			return nil, fmt.Errorf("cannot decompress zstd data of size %d: %w; src_zstd=%X", len(src), err, src)
+			return nil, fmt.Errorf("cannot decompress zstd data: %w", err)
 		}
 		dst, err = unmarshalInt64NearestDelta(dst, bb.B, firstValue, itemsCount)
 		bbPool.Put(bb)
@@ -178,7 +178,7 @@ func unmarshalInt64Array(dst []int64, src []byte, mt MarshalType, firstValue int
 		bb := bbPool.Get()
 		bb.B, err = DecompressZSTD(bb.B[:0], src)
 		if err != nil {
-			return nil, fmt.Errorf("cannot decompress zstd data of size %d: %w; src_zstd=%X", len(src), err, src)
+			return nil, fmt.Errorf("cannot decompress zstd data: %w", err)
 		}
 		dst, err = unmarshalInt64NearestDelta2(dst, bb.B, firstValue, itemsCount)
 		bbPool.Put(bb)
diff --git a/lib/mergeset/block_stream_reader.go b/lib/mergeset/block_stream_reader.go
index 0949c507f..a89710887 100644
--- a/lib/mergeset/block_stream_reader.go
+++ b/lib/mergeset/block_stream_reader.go
@@ -267,7 +267,7 @@ func (bsr *blockStreamReader) readNextBHS() error {
 	var err error
 	bsr.unpackedBuf, err = encoding.DecompressZSTD(bsr.unpackedBuf[:0], bsr.packedBuf)
 	if err != nil {
-		return fmt.Errorf("cannot decompress index block with size %d: %w", mr.indexBlockSize, err)
+		return fmt.Errorf("cannot decompress index block: %w", err)
 	}
 
 	// Unmarshal the unpacked index block into bsr.bhs.
diff --git a/lib/mergeset/metaindex_row.go b/lib/mergeset/metaindex_row.go
index 27569a321..3d5b07fe9 100644
--- a/lib/mergeset/metaindex_row.go
+++ b/lib/mergeset/metaindex_row.go
@@ -89,7 +89,7 @@ func unmarshalMetaindexRows(dst []metaindexRow, r io.Reader) ([]metaindexRow, er
 	}
 	data, err := encoding.DecompressZSTD(nil, compressedData)
 	if err != nil {
-		return dst, fmt.Errorf("cannot decompress metaindex data with size %d bytes: %w", len(compressedData), err)
+		return dst, fmt.Errorf("cannot decompress metaindex data: %w", err)
 	}
 
 	dstLen := len(dst)
diff --git a/lib/mergeset/part_search.go b/lib/mergeset/part_search.go
index 01d067688..79ed0968f 100644
--- a/lib/mergeset/part_search.go
+++ b/lib/mergeset/part_search.go
@@ -294,7 +294,7 @@ func (ps *partSearch) readIndexBlock(mr *metaindexRow) (*indexBlock, error) {
 	var err error
 	ps.indexBuf, err = encoding.DecompressZSTD(ps.indexBuf[:0], ps.compressedIndexBuf)
 	if err != nil {
-		return nil, fmt.Errorf("cannot decompress index block with size %d bytes: %w", len(ps.compressedIndexBuf), err)
+		return nil, fmt.Errorf("cannot decompress index block: %w", err)
 	}
 	idxb := getIndexBlock()
 	idxb.bhs, err = unmarshalBlockHeaders(idxb.bhs[:0], ps.indexBuf, int(mr.blockHeadersCount))