request only 1 best version for latest version resolution (#14625)

ListObjects, ListObjectsV2 calls are being heavily taxed when
there are many versions on objects left over from a previous
release or ILM was never setup to clean them up. Instead
of being absolutely correct at resolving the exact latest
version of an object, we simply rely on the top most 1
version and resolve the rest.

Once we have obtained the top most "1" version for
ListObject, ListObjectsV2 call we break out.

cmd/xl-storage-format-v2.go

@@ -1691,7 +1691,7 @@ func (x xlMetaV2) ListVersions(volume, path string) ([]FileInfo, error) {
 // Quorum must be the minimum number of matching metadata files.
 // Quorum should be > 1 and <= len(versions).
 // If strict is set to false, entries that match type
-func mergeXLV2Versions(quorum int, strict bool, versions ...[]xlMetaV2ShallowVersion) (merged []xlMetaV2ShallowVersion) {
+func mergeXLV2Versions(quorum int, strict bool, requestedVersions int, versions ...[]xlMetaV2ShallowVersion) (merged []xlMetaV2ShallowVersion) {
 	if quorum <= 0 {
 		quorum = 1
 	}
@@ -1708,6 +1708,8 @@ func mergeXLV2Versions(quorum int, strict bool, versions ...[]xlMetaV2ShallowVer
 	// Shallow copy input
 	versions = append(make([][]xlMetaV2ShallowVersion, 0, len(versions)), versions...)
 
+	var nVersions int // captures all non-free versions
+
 	// Our result
 	merged = make([]xlMetaV2ShallowVersion, 0, len(versions[0]))
 	tops := make([]xlMetaV2ShallowVersion, len(versions))
@@ -1744,6 +1746,12 @@ func mergeXLV2Versions(quorum int, strict bool, versions ...[]xlMetaV2ShallowVer
 			latest = tops[0]
 			latestCount = len(tops)
 			merged = append(merged, latest)
+
+			// Calculate latest 'n' non-free versions.
+			if !latest.header.FreeVersion() {
+				nVersions++
+			}
+
 		} else {
 			// Find latest.
 			for i, ver := range tops {
@@ -1807,6 +1815,11 @@ func mergeXLV2Versions(quorum int, strict bool, versions ...[]xlMetaV2ShallowVer
 			}
 			if latestCount >= quorum {
 				merged = append(merged, latest)
+
+				// Calculate latest 'n' non-free versions.
+				if !latest.header.FreeVersion() {
+					nVersions++
+				}
 			}
 		}
 
@@ -1840,7 +1853,13 @@ func mergeXLV2Versions(quorum int, strict bool, versions ...[]xlMetaV2ShallowVer
 				break
 			}
 		}
+
+		if requestedVersions > 0 && requestedVersions == nVersions {
+			merged = append(merged, versions[0]...)
+			break
+		}
 	}
+
 	// Sanity check. Enable if duplicates show up.
 	if false {
 		found := make(map[[16]byte]struct{})