Deprecate and remove in-memory object caching (#5481)

in-memory caching cannot be cleanly implemented
without the access to GC which Go doesn't naturally
provide. At times we have seen that object caching
is more of an hindrance rather than a boon for
our use cases.

Removing it completely from our implementation
  related to #5160 and #5182

cmd/xl-v1.go

@@ -18,15 +18,12 @@ package cmd
 
 import (
 	"fmt"
-	"runtime/debug"
 	"sort"
 	"sync"
 	"time"
 
-	humanize "github.com/dustin/go-humanize"
 	"github.com/minio/minio/pkg/disk"
 	"github.com/minio/minio/pkg/errors"
-	"github.com/minio/minio/pkg/objcache"
 )
 
 // XL constants.
@@ -37,9 +34,6 @@ const (
 	// Uploads metadata file carries per multipart object metadata.
 	uploadsJSONFile = "uploads.json"
 
-	// Represents the minimum required RAM size to enable caching.
-	minRAMSize = 24 * humanize.GiByte
-
 	// Maximum erasure blocks.
 	maxErasureBlocks = 16
 
@@ -55,12 +49,6 @@ type xlObjects struct {
 	// ListObjects pool management.
 	listPool *treeWalkPool
 
-	// Object cache for caching objects.
-	objCache *objcache.Cache
-
-	// Object cache enabled.
-	objCacheEnabled bool
-
 	// name space mutex for object layer
 	nsMutex *nsLockMap
 }
@@ -112,28 +100,6 @@ func newXLObjects(storageDisks []StorageAPI) (ObjectLayer, error) {
 		listPool:     listPool,
 		nsMutex:      newNSLock(globalIsDistXL),
 	}
-	// Get cache size if _MINIO_CACHE environment variable is set.
-	var maxCacheSize uint64
-	if !globalXLObjCacheDisabled {
-		maxCacheSize, err = GetMaxCacheSize()
-		errorIf(err, "Unable to get maximum cache size")
-
-		// Enable object cache if cache size is more than zero
-		xl.objCacheEnabled = maxCacheSize > 0
-	}
-
-	// Check if object cache is enabled.
-	if xl.objCacheEnabled {
-		// Initialize object cache.
-		objCache, oerr := objcache.New(maxCacheSize, objcache.DefaultExpiry)
-		if oerr != nil {
-			return nil, oerr
-		}
-		objCache.OnEviction = func(key string) {
-			debug.FreeOSMemory()
-		}
-		xl.objCache = objCache
-	}
 
 	// Initialize meta volume, if volume already exists ignores it.
 	if err = initMetaVolume(xl.storageDisks); err != nil {