Make no grouping the default

Bats tests were hanging does to CGO pathological case

go/cmd/dolt/commands/admin/archive.go

@@ -48,11 +48,11 @@ var docs = cli.CommandDocumentationContent{
 table files into archives. Currently, for safety, table files are left in place.`,
 
 	Synopsis: []string{
-		`[--no-grouping]`,
+		`[--group-chunks]`,
 	},
 }
 
-const noGroupingFlag = "no-grouping"
+const groupChunksFlag = "group-chunks"
 
 // Description returns a description of the command
 func (cmd ArchiveCmd) Description() string {
@@ -68,7 +68,7 @@ func (cmd ArchiveCmd) Docs() *cli.CommandDocumentation {
 
 func (cmd ArchiveCmd) ArgParser() *argparser.ArgParser {
 	ap := argparser.NewArgParserWithMaxArgs(cmd.Name(), 0)
-	ap.SupportsFlag(noGroupingFlag, "", "Do not attempt to group chunks. Default dictionary will be used for all chunks")
+	ap.SupportsFlag(groupChunksFlag, "", "Attempt to group chunks. This will produce smaller archives, but can take much longer to build.")
 	/* TODO: Implement these flags
 	ap.SupportsFlag("purge", "", "remove table files after archiving")
 	ap.SupportsFlag("revert", "", "Return to unpurged table files, or rebuilt table files from archives")
@@ -104,7 +104,7 @@ func (cmd ArchiveCmd) Exec(ctx context.Context, commandStr string, args []string
 	})
 
 	groupings := nbs.NewChunkRelations()
-	if !apr.Contains(noGroupingFlag) {
+	if apr.Contains(groupChunksFlag) {
 		err = historicalFuzzyMatching(ctx, hs, &groupings, dEnv.DoltDB)
 		if err != nil {
 			cli.PrintErrln(err)

go/store/nbs/archive_build.go

@@ -528,14 +528,17 @@ func (cg *chunkGroup) worstZScore() float64 {
 // rebuild - recalculate the entire group's compression ratio. Dictionary and total compression ratio are updated as well.
 // This method is called after a new chunk is added to the group. Ensures that stats about the group are up-to-date.
 func (cg *chunkGroup) rebuild(ctx context.Context, chunkCache *SimpleChunkSourceCache, defaultDict *gozstd.CDict, stats *Stats) error {
-	chks := make([]*chunks.Chunk, len(cg.chks))
+	chks := make([]*chunks.Chunk, 0, len(cg.chks))
 
-	for i, cs := range cg.chks {
+	for _, cs := range cg.chks {
 		chk, err := chunkCache.get(ctx, cs.chunkId, stats)
 		if err != nil {
 			return err
 		}
-		chks[i] = chk
+		if chk == nil {
+			continue
+		}
+		chks = append(chks, chk)
 	}
 
 	totalBytes := 0
@@ -798,13 +801,14 @@ func newSimpleChunkSourceCache(cs chunkSource) (*SimpleChunkSourceCache, error)
 }
 
 // get a chunk from the cache. If the chunk is not in the cache, it will be fetched from the ChunkSource.
+// If the ChunkSource doesn't have the chunk, return nil - this is a valid case.
 func (csc *SimpleChunkSourceCache) get(ctx context.Context, h hash.Hash, stats *Stats) (*chunks.Chunk, error) {
 	if chk, ok := csc.cache.Get(h); ok {
 		return chk, nil
 	}
 
 	bytes, err := csc.cs.get(ctx, h, stats)
-	if err != nil {
+	if bytes == nil || err != nil {
 		return nil, err
 	}
 

go/store/nbs/archive_writer.go

@@ -105,7 +105,7 @@ func (aw *archiveWriter) writeByteSpan(b []byte) (uint32, error) {
 	}
 
 	if len(b) == 0 {
-		return 0, nil
+		return 0, fmt.Errorf("Rutime error: empty compressed byte span")
 	}
 
 	offset := aw.bytesWritten