Feature/db read entry - read entry/s using simple union sql, instead …

…of the complex views/sqEntriesLineage (#783)

catalog/cataloger_diff.go

@@ -206,7 +206,7 @@ func (c *cataloger) diffFromChild(ctx context.Context, tx db.Tx, childID, parent
 		parentEffectiveQuery, args, err := psql.Select("commit_id as parent_effective_commit").
 			From("catalog_commits").
 			Where("branch_id = ? AND merge_source_branch = ?", childID, parentID).
-			OrderBy("commit_id").
+			OrderBy("commit_id desc").
 			Limit(1).
 			ToSql()
 		if err != nil {

catalog/db_batch_entry_read.go

@@ -123,25 +123,20 @@ func (c *cataloger) readEntriesBatch(wg *sync.WaitGroup, inputBatchChan chan bat
 
 func (c *cataloger) dbSelectBatchEntries(repository string, ref Ref, pathReqList []pathRequest) ([]*Entry, error) {
 	res, err := c.db.Transact(func(tx db.Tx) (interface{}, error) {
-		// get branch
 		branchID, err := c.getBranchIDCache(tx, repository, ref.Branch)
 		if err != nil {
 			return nil, err
 		}
-		// get lineage
-		lineage, err := getLineage(tx, branchID, ref.CommitID)
-		if err != nil {
-			return nil, fmt.Errorf("get lineage: %w", err)
-		}
 		// prepare list of paths
 		p := make([]string, len(pathReqList))
 		for i, s := range pathReqList {
 			p[i] = s.path
 		}
 		// prepare query
-		readExpr := sq.Select("path", "physical_address", "creation_date", "size", "checksum", "metadata", "is_expired").
-			FromSelect(sqEntriesLineage(branchID, ref.CommitID, lineage), "entries").
-			Where(sq.And{sq.Eq{"path": p}, sq.Expr("not is_deleted")})
+		readExpr, err := sqEntryLineageSelect(tx, branchID, ref.CommitID, true, p)
+		if err != nil {
+			return nil, fmt.Errorf("lineage select: %w", err)
+		}
 		query, args, err := readExpr.PlaceholderFormat(sq.Dollar).ToSql()
 		if err != nil {
 			return nil, fmt.Errorf("build sql: %w", err)

catalog/db_read_entry.go

@@ -0,0 +1,69 @@
+package catalog
+
+import (
+	"strconv"
+
+	sq "github.com/Masterminds/squirrel"
+	"github.com/treeverse/lakefs/db"
+)
+
+// sqEntryLineageSelect select path/s from a branch, including lineage
+// 1. Union all the branches in the lineage.
+// 2. if multiple branches have this path - select the one closest to the requested branch
+// 3. filterDeleted param = true will remove results that were deleted
+func sqEntryLineageSelect(tx db.Tx, branchID int64, commitID CommitID, filterDeleted bool, paths []string) (sq.SelectBuilder, error) {
+	lineage, err := getLineage(tx, branchID, commitID)
+	if err != nil {
+		return sq.SelectBuilder{}, err
+	}
+	unionSelect := sqEntryBranchSelect(branchID, commitID, paths).Column("? as lineage_order", "0").
+		Prefix("(").Suffix(")")
+	for i, branch := range lineage {
+		unionSelect = unionSelect.SuffixExpr(sq.ConcatExpr(
+			" UNION ALL (",
+			sqEntryBranchSelect(branch.BranchID, branch.CommitID, paths).Column("? as lineage_order", strconv.Itoa(i+1)),
+			")"))
+	}
+	distinctSelect := sq.Select("*").
+		FromSelect(unionSelect, "c").
+		Distinct().Options("ON (path)").
+		OrderBy("path", "lineage_order")
+	finalSelect := sq.Select("path", "physical_address", "creation_date", "size", "checksum", "metadata", "is_expired").
+		FromSelect(distinctSelect, "t")
+	if filterDeleted {
+		finalSelect = finalSelect.Where("max_commit = ?", MaxCommitID)
+	}
+	return finalSelect, nil
+}
+
+// sqEntryBranchSelect select path/s from a single branch.
+// 1. Get the requested commit
+// 2. If a path has multiple versions in various commits - Return the row with highest min commit
+// 3. If the version was deleted after the requested commit - the row max-commit will be set to uncommitted
+func sqEntryBranchSelect(branchID int64, commitID CommitID, paths []string) sq.SelectBuilder {
+	rawSelect := sq.Select("path", "physical_address", "creation_date", "size", "checksum", "metadata", "is_expired").
+		Distinct().Options("ON (branch_id,path)").
+		From("catalog_entries").
+		Where("branch_id = ?", branchID).
+		OrderBy("branch_id", "path", "min_commit desc")
+	l := len(paths)
+	// the case of single path is handled differently than multiple pathes because my tests showed there is a significant
+	// difference between (about 25%) between "where path = X" and "where path in (X)". even though the optimization is
+	// the same. may be a driver issue in the client application
+	if l == 1 {
+		rawSelect = rawSelect.Where("path = ?", paths[0])
+	} else {
+		rawSelect = rawSelect.Where(sq.Eq{"path": paths})
+	}
+	switch commitID {
+	case CommittedID:
+		rawSelect = rawSelect.Where("min_commit < ?", MaxCommitID).
+			Column("max_commit")
+	case UncommittedID:
+		rawSelect = rawSelect.Column("max_commit")
+	default:
+		rawSelect = rawSelect.Where("min_commit between 1 and ?", commitID).
+			Column("CASE WHEN max_commit >= ? THEN ? ELSE max_commit END AS max_commit", commitID, MaxCommitID)
+	}
+	return rawSelect
+}

catalog/views.go

@@ -146,14 +146,14 @@ func sqDiffFromChildV(parentID, childID int64, parentEffectiveCommit, childEffec
 		FromSelect(RemoveNonRelevantQ, "t1")
 }
 
-func sqDiffFromParentV(parentID, childID int64, lastChildMergeWithParent CommitID, parentUncommittedLineage, childUncommittedLineage []lineageCommit) sq.SelectBuilder {
+func sqDiffFromParentV(parentID, childID int64, lastChildMergeWithParent CommitID, parentCommittedLineage, childUncommittedLineage []lineageCommit) sq.SelectBuilder {
 	childLineageValues := getLineageAsValues(childUncommittedLineage, childID, MaxCommitID)
 	childLineage := sqEntriesLineage(childID, UncommittedID, childUncommittedLineage)
 	sqChild := sq.Select("*").
 		FromSelect(childLineage, "s").
 		Where("displayed_branch = ?", childID)
 
-	parentLineage := sqEntriesLineage(parentID, CommittedID, parentUncommittedLineage)
+	parentLineage := sqEntriesLineage(parentID, CommittedID, parentCommittedLineage)
 	// Can diff with expired files, just not usefully!
 	internalV := sq.Select("f.path",
 		"f.entry_ctid",