XL/PutObject: Add single putObject and multipart caching. (#2115)

- Additionally adds test cases as well for object cache.
- Adds auto-expiry with expiration and cleanup time interval.

Fixes #2080
Fixes #2091

docs/caching.md

@@ -0,0 +1,39 @@
+## Object caching
+
+Object caching by turned on by default with following settings
+
+  - Default cache size 8GB, can be changed from environment variable
+    ``MINIO_CACHE_SIZE`` supports both SI and ISO IEC standard forms
+    for input size parameters.
+
+  - Default expiration of entries is 72 hours, can be changed from
+    environment variable ``MINIO_CACHE_EXPIRY`` supportings Go
+    ``time.Duration`` with valid units  "ns", "us" (or "µs"),
+    "ms", "s", "m", "h".
+
+  - Default expiry interval is 1/4th of the expiration hours, so
+    expiration sweep happens across the cache every 1/4th the time
+    duration of the set entry expiration duration.
+
+### Tricks
+
+Setting MINIO_CACHE_SIZE=0 will turn off caching entirely.
+Setting MINIO_CACHE_EXPIRY=0s will turn off cache garbage collections,
+all cached objects will never expire.
+
+### Behavior
+
+Caching happens for both GET and PUT.
+
+- GET caches new objects for entries not found in cache,
+otherwise serves from the cache.
+
+- PUT/POST caches all successfully uploaded objects.
+
+NOTE: Cache is not populated if there are any errors
+      while reading from the disk.
+
+Expiration happens automatically based on the configured
+interval as explained above, frequently accessed objects
+stay alive for significantly longer time due to the fact
+that expiration time is reset for every cache hit.

globals.go

@@ -16,7 +16,10 @@
 
 package main
 
-import "github.com/fatih/color"
+import (
+	"github.com/fatih/color"
+	"github.com/minio/minio/pkg/objcache"
+)
 
 // Global constants for Minio.
 const (
@@ -45,6 +48,8 @@ var (
 	globalMaxConn = 0
 	// Maximum cache size.
 	globalMaxCacheSize = uint64(maxCacheSize)
+	// Cache expiry.
+	globalCacheExpiry = objcache.DefaultExpiry
 	// Add new variable global values here.
 )
 

namespace-lock.go

@@ -29,7 +29,7 @@ type nsParam struct {
 
 // nsLock - provides primitives for locking critical namespace regions.
 type nsLock struct {
-	*sync.RWMutex
+	sync.RWMutex
 	ref uint
 }
 
@@ -37,7 +37,7 @@ type nsLock struct {
 // Unlock, RLock and RUnlock.
 type nsLockMap struct {
 	lockMap map[nsParam]*nsLock
-	mutex   *sync.Mutex
+	mutex   sync.Mutex
 }
 
 // Global name space lock.
@@ -47,7 +47,6 @@ var nsMutex *nsLockMap
 func initNSLock() {
 	nsMutex = &nsLockMap{
 		lockMap: make(map[nsParam]*nsLock),
-		mutex:   &sync.Mutex{},
 	}
 }
 
@@ -59,7 +58,6 @@ func (n *nsLockMap) lock(volume, path string, readLock bool) {
 	nsLk, found := n.lockMap[param]
 	if !found {
 		nsLk = &nsLock{
-			RWMutex: &sync.RWMutex{},
 			ref: 0,
 		}
 		n.lockMap[param] = nsLk

pkg/objcache/README.md

@@ -0,0 +1,62 @@
+```
+PACKAGE DOCUMENTATION
+
+package objcache
+    import "github.com/minio/minio/pkg/objcache"
+
+    Package objcache implements in memory caching methods.
+
+VARIABLES
+
+var DefaultExpiry = time.Duration(72 * time.Hour) // 72hrs.
+
+    DefaultExpiry represents default time duration value when individual
+    entries will be expired.
+
+var ErrCacheFull = errors.New("Not enough space in cache")
+    ErrCacheFull - cache is full.
+
+var ErrKeyNotFoundInCache = errors.New("Key not found in cache")
+    ErrKeyNotFoundInCache - key not found in cache.
+
+var NoExpiry = time.Duration(0)
+    NoExpiry represents caches to be permanent and can only be deleted.
+
+TYPES
+
+type Cache struct {
+
+    // OnEviction - callback function for eviction
+    OnEviction func(key string)
+    // contains filtered or unexported fields
+}
+    Cache holds the required variables to compose an in memory cache system
+    which also provides expiring key mechanism and also maxSize.
+
+func New(maxSize uint64, expiry time.Duration) *Cache
+    New - Return a new cache with a given default expiry duration. If the
+    expiry duration is less than one (or NoExpiry), the items in the cache
+    never expire (by default), and must be deleted manually.
+
+func (c *Cache) Create(key string, size int64) (w io.WriteCloser, err error)
+    Create - validates if object size fits with in cache size limit and
+    returns a io.WriteCloser to which object contents can be written and
+    finally Close()'d. During Close() we checks if the amount of data
+    written is equal to the size of the object, in which case it saves the
+    contents to object cache.
+
+func (c *Cache) Delete(key string)
+    Delete - delete deletes an entry from the cache.
+
+func (c *Cache) DeleteExpired()
+    DeleteExpired - deletes all the expired entries from the cache.
+
+func (c *Cache) Open(key string) (io.ReadSeeker, error)
+    Open - open the in-memory file, returns an in memory read seeker.
+    returns an error ErrNotFoundInCache, if the key does not exist.
+
+func (c *Cache) StopExpiry()
+    StopExpiry sends a message to the expiry routine to stop expiring cached
+    entries. NOTE: once this is called, cached entries will not be expired
+    if the consume has called this.
+```

pkg/objcache/objcache.go

@@ -26,15 +26,25 @@ import (
 	"time"
 )
 
-// NoExpiration represents caches to be permanent and can only be deleted.
-var NoExpiration = time.Duration(0)
+// NoExpiry represents caches to be permanent and can only be deleted.
+var NoExpiry = time.Duration(0)
+
+// DefaultExpiry represents default time duration value when individual entries will be expired.
+var DefaultExpiry = time.Duration(72 * time.Hour) // 72hrs.
+
+// buffer represents the in memory cache of a single entry.
+// buffer carries value of the data and last accessed time.
+type buffer struct {
+	value        []byte    // Value of the entry.
+	lastAccessed time.Time // Represents time when value was last accessed.
+}
 
 // Cache holds the required variables to compose an in memory cache system
 // which also provides expiring key mechanism and also maxSize.
 type Cache struct {
 	// Mutex is used for handling the concurrent
 	// read/write requests for cache
-	mutex *sync.RWMutex
+	mutex sync.Mutex
 
 	// maxSize is a total size for overall cache
 	maxSize uint64
@@ -43,29 +53,39 @@ type Cache struct {
 	currentSize uint64
 
 	// OnEviction - callback function for eviction
-	OnEviction func(a ...interface{})
+	OnEviction func(key string)
 
-	// totalEvicted counter to keep track of total expirations
+	// totalEvicted counter to keep track of total expirys
 	totalEvicted int
 
 	// map of objectName and its contents
-	entries map[string][]byte
+	entries map[string]*buffer
 
-	// Expiration in time duration.
+	// Expiry in time duration.
 	expiry time.Duration
+
+	// Stop garbage collection routine, stops any running GC routine.
+	stopGC chan struct{}
 }
 
-// New creates an inmemory cache
-//
-// maxSize is used for expiring objects before we run out of memory
-// expiration is used for expiration of a key from cache
+// New - Return a new cache with a given default expiry duration.
+// If the expiry duration is less than one (or NoExpiry),
+// the items in the cache never expire (by default), and must be deleted
+// manually.
 func New(maxSize uint64, expiry time.Duration) *Cache {
-	return &Cache{
-		mutex:   &sync.RWMutex{},
+	C := &Cache{
 		maxSize: maxSize,
-		entries: make(map[string][]byte),
+		entries: make(map[string]*buffer),
 		expiry:  expiry,
 	}
+	// We have expiry start the janitor routine.
+	if expiry > 0 {
+		C.stopGC = make(chan struct{})
+
+		// Start garbage collection routine to expire objects.
+		C.startGC()
+	}
+	return C
 }
 
 // ErrKeyNotFoundInCache - key not found in cache.
@@ -74,17 +94,19 @@ var ErrKeyNotFoundInCache = errors.New("Key not found in cache")
 // ErrCacheFull - cache is full.
 var ErrCacheFull = errors.New("Not enough space in cache")
 
+// ErrExcessData - excess data was attempted to be written on cache.
+var ErrExcessData = errors.New("Attempted excess write on cache")
+
 // Used for adding entry to the object cache. Implements io.WriteCloser
 type cacheBuffer struct {
 	*bytes.Buffer // Implements io.Writer
-	onClose       func()
+	onClose       func() error
 }
 
 // On close, onClose() is called which checks if all object contents
 // have been written so that it can save the buffer to the cache.
-func (c cacheBuffer) Close() error {
-	c.onClose()
-	return nil
+func (c cacheBuffer) Close() (err error) {
+	return c.onClose()
 }
 
 // Create - validates if object size fits with in cache size limit and returns a io.WriteCloser
@@ -92,39 +114,43 @@ func (c cacheBuffer) Close() error {
 // checks if the amount of data written is equal to the size of the object, in which
 // case it saves the contents to object cache.
 func (c *Cache) Create(key string, size int64) (w io.WriteCloser, err error) {
-	c.mutex.Lock()
-	defer c.mutex.Unlock()
+	// Recovers any panic generated and return errors appropriately.
+	defer func() {
+		if r := recover(); r != nil {
+			// Recover any panic and return ErrCacheFull.
+			err = ErrCacheFull
+		}
+	}() // Do not crash the server.
 
 	valueLen := uint64(size)
-	if c.maxSize > 0 {
 	// Check if the size of the object is not bigger than the capacity of the cache.
-		if valueLen > c.maxSize {
+	if c.maxSize > 0 && valueLen > c.maxSize {
 		return nil, ErrCacheFull
 	}
-		// TODO - auto expire random key.
-		if c.currentSize+valueLen > c.maxSize {
-			return nil, ErrCacheFull
-		}
-	}
 
 	// Will hold the object contents.
 	buf := bytes.NewBuffer(make([]byte, 0, size))
-	// Account for the memory allocated above.
-	c.currentSize += uint64(size)
 
 	// Function called on close which saves the object contents
 	// to the object cache.
-	onClose := func() {
+	onClose := func() error {
 		c.mutex.Lock()
 		defer c.mutex.Unlock()
-		if buf.Len() != int(size) {
+		if size != int64(buf.Len()) {
 			// Full object not available hence do not save buf to object cache.
-			c.currentSize -= uint64(size)
-			return
+			return io.ErrShortBuffer
+		}
+		if c.maxSize > 0 && c.currentSize+valueLen > c.maxSize {
+			return ErrExcessData
 		}
 		// Full object available in buf, save it to cache.
-		c.entries[key] = buf.Bytes()
-		return
+		c.entries[key] = &buffer{
+			value:        buf.Bytes(),
+			lastAccessed: time.Now().UTC(), // Save last accessed time.
+		}
+		// Account for the memory allocated above.
+		c.currentSize += uint64(size)
+		return nil
 	}
 
 	// Object contents that is written - cacheBuffer.Write(data)
@@ -138,35 +164,77 @@ func (c *Cache) Create(key string, size int64) (w io.WriteCloser, err error) {
 // Open - open the in-memory file, returns an in memory read seeker.
 // returns an error ErrNotFoundInCache, if the key does not exist.
 func (c *Cache) Open(key string) (io.ReadSeeker, error) {
-	c.mutex.RLock()
-	defer c.mutex.RUnlock()
-
 	// Entry exists, return the readable buffer.
-	buffer, ok := c.entries[key]
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	buf, ok := c.entries[key]
 	if !ok {
 		return nil, ErrKeyNotFoundInCache
 	}
-	return bytes.NewReader(buffer), nil
+	buf.lastAccessed = time.Now().UTC()
+	return bytes.NewReader(buf.value), nil
 }
 
-// Delete - delete deletes an entry from in-memory fs.
+// Delete - delete deletes an entry from the cache.
 func (c *Cache) Delete(key string) {
 	c.mutex.Lock()
-	defer c.mutex.Unlock()
+	c.delete(key)
+	c.mutex.Unlock()
+	if c.OnEviction != nil {
+		c.OnEviction(key)
+	}
+}
 
-	// Delete an entry.
-	buffer, ok := c.entries[key]
-	if ok {
-		c.deleteEntry(key, int64(len(buffer)))
+// gc - garbage collect all the expired entries from the cache.
+func (c *Cache) gc() {
+	var evictedEntries []string
+	c.mutex.Lock()
+	for k, v := range c.entries {
+		if c.expiry > 0 && time.Now().UTC().Sub(v.lastAccessed) > c.expiry {
+			c.delete(k)
+			evictedEntries = append(evictedEntries, k)
+		}
+	}
+	c.mutex.Unlock()
+	for _, k := range evictedEntries {
+		if c.OnEviction != nil {
+			c.OnEviction(k)
+		}
+	}
+}
+
+// StopGC sends a message to the expiry routine to stop
+// expiring cached entries. NOTE: once this is called, cached
+// entries will not be expired if the consumer has called this.
+func (c *Cache) StopGC() {
+	if c.stopGC != nil {
+		c.stopGC <- struct{}{}
 	}
 }
 
-// Deletes the entry that was found.
-func (c *Cache) deleteEntry(key string, size int64) {
+// startGC starts running a routine ticking at expiry interval, on each interval
+// this routine does a sweep across the cache entries and garbage collects all the
+// expired entries.
+func (c *Cache) startGC() {
+	go func() {
+		for {
+			select {
+			// Wait till cleanup interval and initiate delete expired entries.
+			case <-time.After(c.expiry / 4):
+				c.gc()
+				// Stop the routine, usually called by the user of object cache during cleanup.
+			case <-c.stopGC:
+				return
+			}
+		}
+	}()
+}
+
+// Deletes a requested entry from the cache.
+func (c *Cache) delete(key string) {
+	if buf, ok := c.entries[key]; ok {
 		delete(c.entries, key)
-	c.currentSize -= uint64(size)
+		c.currentSize -= uint64(len(buf.value))
 		c.totalEvicted++
-	if c.OnEviction != nil {
-		c.OnEviction(key)
 	}
 }

pkg/objcache/objcache_test.go

@@ -0,0 +1,172 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package objcache
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"testing"
+	"time"
+)
+
+// TestObjCache - tests various cases for object cache behavior.
+func TestObjCache(t *testing.T) {
+	// Non exhaustive list of all object cache behavior cases.
+	testCases := []struct {
+		expiry    time.Duration
+		cacheSize uint64
+		err       error
+		closeErr  error
+	}{
+		// Validate if a key is not found in cache and Open fails.
+		{
+			expiry:    NoExpiry,
+			cacheSize: 1024,
+			err:       ErrKeyNotFoundInCache,
+		},
+		// Validate if cache indicates that it is full and Create fails.
+		{
+			expiry:    NoExpiry,
+			cacheSize: 1,
+			err:       ErrCacheFull,
+		},
+		// Validate if Create succeeds but Close fails to write to buffer.
+		{
+			expiry:    NoExpiry,
+			cacheSize: 2,
+			closeErr:  io.ErrShortBuffer,
+		},
+		// Validate that Create and Close succeed, making sure to update the cache.
+		{
+			expiry:    NoExpiry,
+			cacheSize: 1024,
+		},
+		// Validate that Delete succeeds and Open fails with key not found in cache.
+		{
+			expiry:    NoExpiry,
+			cacheSize: 1024,
+			err:       ErrKeyNotFoundInCache,
+		},
+		// Validate OnEviction function is called upon entry delete.
+		{
+			expiry:    NoExpiry,
+			cacheSize: 1024,
+		},
+	}
+
+	// Test 1 validating Open failure.
+	testCase := testCases[0]
+	cache := New(testCase.cacheSize, testCase.expiry)
+	_, err := cache.Open("test")
+	if testCase.err != err {
+		t.Errorf("Test case 2 expected to pass, failed instead %s", err)
+	}
+
+	// Test 2 validating Create failure.
+	testCase = testCases[1]
+	cache = New(testCase.cacheSize, testCase.expiry)
+	_, err = cache.Create("test", 2)
+	if testCase.err != err {
+		t.Errorf("Test case 2 expected to pass, failed instead %s", err)
+	}
+
+	// Test 3 validating Create succeeds and returns a writer.
+	// Subsequently we Close() without writing any data, to receive
+	// `io.ErrShortBuffer`
+	testCase = testCases[2]
+	cache = New(testCase.cacheSize, testCase.expiry)
+	w, err := cache.Create("test", 1)
+	if testCase.err != err {
+		t.Errorf("Test case 3 expected to pass, failed instead %s", err)
+	}
+	if err = w.Close(); err != testCase.closeErr {
+		t.Errorf("Test case 3 expected to pass, failed instead %s", err)
+	}
+
+	// Test 4 validates Create and Close succeeds successfully caching
+	// the writes.
+	testCase = testCases[3]
+	cache = New(testCase.cacheSize, testCase.expiry)
+	w, err = cache.Create("test", 5)
+	if testCase.err != err {
+		t.Errorf("Test case 4 expected to pass, failed instead %s", err)
+	}
+	// Write '5' bytes.
+	w.Write([]byte("Hello"))
+	// Close to successfully save into cache.
+	if err = w.Close(); err != nil {
+		t.Errorf("Test case 4 expected to pass, failed instead %s", err)
+	}
+	r, err := cache.Open("test")
+	if err != nil {
+		t.Errorf("Test case 4 expected to pass, failed instead %s", err)
+	}
+	// Reads everything stored for key "test".
+	cbytes, err := ioutil.ReadAll(r)
+	if err != nil {
+		t.Errorf("Test case 4 expected to pass, failed instead %s", err)
+	}
+	// Validate if read bytes match.
+	if !bytes.Equal(cbytes, []byte("Hello")) {
+		t.Errorf("Test case 4 expected to pass. wanted \"Hello\", got %s", string(cbytes))
+	}
+
+	// Test 5 validates Delete succeeds and Open fails with err
+	testCase = testCases[4]
+	cache = New(testCase.cacheSize, testCase.expiry)
+	w, err = cache.Create("test", 5)
+	if err != nil {
+		t.Errorf("Test case 5 expected to pass, failed instead %s", err)
+	}
+	// Write '5' bytes.
+	w.Write([]byte("Hello"))
+	// Close to successfully save into cache.
+	if err = w.Close(); err != nil {
+		t.Errorf("Test case 5 expected to pass, failed instead %s", err)
+	}
+	// Delete the cache entry.
+	cache.Delete("test")
+	_, err = cache.Open("test")
+	if testCase.err != err {
+		t.Errorf("Test case 5 expected to pass, failed instead %s", err)
+	}
+
+	// Test 6 validates OnEviction being called upon Delete is being invoked.
+	testCase = testCases[5]
+	cache = New(testCase.cacheSize, testCase.expiry)
+	w, err = cache.Create("test", 5)
+	if err != nil {
+		t.Errorf("Test case 6 expected to pass, failed instead %s", err)
+	}
+	// Write '5' bytes.
+	w.Write([]byte("Hello"))
+	// Close to successfully save into cache.
+	if err = w.Close(); err != nil {
+		t.Errorf("Test case 6 expected to pass, failed instead %s", err)
+	}
+	var deleteKey string
+	cache.OnEviction = func(key string) {
+		deleteKey = key
+	}
+	// Delete the cache entry.
+	cache.Delete("test")
+	if deleteKey != "test" {
+		t.Errorf("Test case 6 expected to pass, wanted \"test\", got %s", deleteKey)
+	}
+}

server-main.go

@@ -149,6 +149,14 @@ func initServerConfig(c *cli.Context) {
 		fatalIf(err, "Unable to convert MINIO_CACHE_SIZE=%s environment variable into its integer value.", maxCacheSizeStr)
 	}
 
+	// Fetch cache expiry from environment variable.
+	if cacheExpiryStr := os.Getenv("MINIO_CACHE_EXPIRY"); cacheExpiryStr != "" {
+		// We need to parse cache expiry to its time.Duration value.
+		var err error
+		globalCacheExpiry, err = time.ParseDuration(cacheExpiryStr)
+		fatalIf(err, "Unable to convert MINIO_CACHE_EXPIRY=%s environment variable into its time.Duration value.", cacheExpiryStr)
+	}
+
 	// Fetch access keys from environment variables if any and update the config.
 	accessKey := os.Getenv("MINIO_ACCESS_KEY")
 	secretKey := os.Getenv("MINIO_SECRET_KEY")

xl-v1-multipart.go

@@ -21,6 +21,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"path"
 	"path/filepath"
 	"strings"
@@ -683,7 +684,19 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 	}
 	// Hold write lock on the destination before rename.
 	nsMutex.Lock(bucket, object)
-	defer nsMutex.Unlock(bucket, object)
+	defer func() {
+		// A new complete multipart upload invalidates any
+		// previously cached object in memory.
+		xl.objCache.Delete(path.Join(bucket, object))
+
+		// This lock also protects the cache namespace.
+		nsMutex.Unlock(bucket, object)
+
+		// Prefetch the object from disk by triggerring a fake GetObject call
+		// Unlike a regular single PutObject,  multipart PutObject is comes in
+		// stages and it is harder to cache.
+		go xl.GetObject(bucket, object, 0, objectSize, ioutil.Discard)
+	}()
 
 	// Rename if an object already exists to temporary location.
 	uniqueID := getUUID()

xl-v1-object.go

@@ -114,7 +114,7 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 	mw := writer
 
 	// Object cache enabled block.
-	if xl.objCacheEnabled {
+	if xlMeta.Stat.Size > 0 && xl.objCacheEnabled {
 		// Validate if we have previous cache.
 		cachedBuffer, err := xl.objCache.Open(path.Join(bucket, object))
 		if err == nil { // Cache hit.
@@ -144,9 +144,10 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 				mw = io.MultiWriter(newBuffer, writer)
 				defer newBuffer.Close()
 			}
+			// Ignore error if cache is full, proceed to write the object.
 			if err != nil && err != objcache.ErrCacheFull {
-				// Perhaps cache is full, returns here.
-				return err
+				// For any other error return here.
+				return toObjectErr(err, bucket, object)
 			}
 		}
 	}
@@ -170,7 +171,7 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64, length i
 		// Start reading the part name.
 		n, err := erasureReadFile(mw, onlineDisks, bucket, pathJoin(object, partName), partName, eInfos, partOffset, readSize, partSize)
 		if err != nil {
-			return err
+			return toObjectErr(err, bucket, object)
 		}
 
 		totalBytesRead += n
@@ -340,7 +341,7 @@ func (xl xlObjects) renameObject(srcBucket, srcObject, dstBucket, dstObject stri
 // until EOF, erasure codes the data across all disk and additionally
 // writes `xl.json` which carries the necessary metadata for future
 // object operations.
-func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.Reader, metadata map[string]string) (string, error) {
+func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.Reader, metadata map[string]string) (md5Sum string, err error) {
 	// Verify if bucket is valid.
 	if !IsValidBucketName(bucket) {
 		return "", BucketNameInvalid{Bucket: bucket}
@@ -359,14 +360,15 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 	if metadata == nil {
 		metadata = make(map[string]string)
 	}
-	nsMutex.Lock(bucket, object)
-	defer nsMutex.Unlock(bucket, object)
-
 	uniqueID := getUUID()
 	tempErasureObj := path.Join(tmpMetaPrefix, uniqueID, "part.1")
 	minioMetaTmpBucket := path.Join(minioMetaBucket, tmpMetaPrefix)
 	tempObj := uniqueID
 
+	// Lock the object.
+	nsMutex.Lock(bucket, object)
+	defer nsMutex.Unlock(bucket, object)
+
 	// Initialize xl meta.
 	xlMeta := newXLMetaV1(object, xl.dataBlocks, xl.parityBlocks)
 
@@ -388,9 +390,33 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 		higherVersion++
 	}
 
+	var mw io.Writer
 	// Initialize md5 writer.
 	md5Writer := md5.New()
 
+	// Proceed to set the cache.
+	var newBuffer io.WriteCloser
+
+	// If caching is enabled, proceed to set the cache.
+	if size > 0 && xl.objCacheEnabled {
+		// PutObject invalidates any previously cached object in memory.
+		xl.objCache.Delete(path.Join(bucket, object))
+
+		// Create a new entry in memory of size.
+		newBuffer, err = xl.objCache.Create(path.Join(bucket, object), size)
+		if err == nil {
+			// Create a multi writer to write to both memory and client response.
+			mw = io.MultiWriter(newBuffer, md5Writer)
+		}
+		// Ignore error if cache is full, proceed to write the object.
+		if err != nil && err != objcache.ErrCacheFull {
+			// For any other error return here.
+			return "", toObjectErr(err, bucket, object)
+		}
+	} else {
+		mw = md5Writer
+	}
+
 	// Limit the reader to its provided size if specified.
 	var limitDataReader io.Reader
 	if size > 0 {
@@ -403,7 +429,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 	}
 
 	// Tee reader combines incoming data stream and md5, data read from input stream is written to md5.
-	teeReader := io.TeeReader(limitDataReader, md5Writer)
+	teeReader := io.TeeReader(limitDataReader, mw)
 
 	// Collect all the previous erasure infos across the disk.
 	var eInfos []erasureInfo
@@ -505,6 +531,12 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 	// Delete the temporary object.
 	xl.deleteObject(minioMetaTmpBucket, newUniqueID)
 
+	// Once we have successfully renamed the object, Close the buffer which would
+	// save the object on cache.
+	if size > 0 && xl.objCacheEnabled && newBuffer != nil {
+		newBuffer.Close()
+	}
+
 	// Return md5sum, successfully wrote object.
 	return newMD5Hex, nil
 }

xl-v1.go

@@ -158,16 +158,20 @@ func newXLObjects(disks []string) (ObjectLayer, error) {
 	// Calculate data and parity blocks.
 	dataBlocks, parityBlocks := len(newPosixDisks)/2, len(newPosixDisks)/2
 
+	// Initialize object cache.
+	objCache := objcache.New(globalMaxCacheSize, globalCacheExpiry)
+
+	// Initialize list pool.
+	listPool := newTreeWalkPool(globalLookupTimeout)
+
 	// Initialize xl objects.
 	xl := xlObjects{
 		physicalDisks:   disks,
 		storageDisks:    newPosixDisks,
 		dataBlocks:      dataBlocks,
 		parityBlocks:    parityBlocks,
-		// Inititalize list pool.
-		listPool: newTreeWalkPool(globalLookupTimeout),
-		// Initialize object caching, FIXME: support auto cache expiration.
-		objCache:        objcache.New(globalMaxCacheSize, objcache.NoExpiration),
+		listPool:        listPool,
+		objCache:        objCache,
 		objCacheEnabled: globalMaxCacheSize > 0,
 	}