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

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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
This commit is contained in:
Harshavardhana
2018-02-02 10:17:13 -08:00
committed by kannappanr
parent 1ebbc2ce88
commit 0c880bb852
15 changed files with 4 additions and 1022 deletions
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64
pkg/objcache/README.md
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@@ -1,64 +0,0 @@
```
PACKAGE DOCUMENTATION
package objcache
import "github.com/minio/minio/pkg/objcache"
Package objcache implements in memory caching methods.
CONSTANTS
const (
// NoExpiry represents caches to be permanent and can only be deleted.
NoExpiry = time.Duration(0)
// DefaultExpiry represents three days time duration when individual entries will be expired.
DefaultExpiry = time.Duration(3 * 24 * time.Hour)
)
VARIABLES
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.
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.
```

50
pkg/objcache/capped-writer.go
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/*
* 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 implements in memory caching methods.
package objcache
// Used for adding entry to the object cache.
// Implements io.WriteCloser
type cappedWriter struct {
offset int64
cap int64
buffer []byte
onClose func() error
}
// Write implements a limited writer, returns error.
// if the writes go beyond allocated size.
func (c *cappedWriter) Write(b []byte) (n int, err error) {
if c.offset+int64(len(b)) > c.cap {
return 0, ErrExcessData
}
n = copy(c.buffer[int(c.offset):int(c.offset)+len(b)], b)
c.offset = c.offset + int64(n)
return n, nil
}
// Reset relinquishes the allocated underlying buffer.
func (c *cappedWriter) Reset() {
c.buffer = nil
}
// 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 cappedWriter) Close() (err error) {
return c.onClose()
}

315
pkg/objcache/objcache.go
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/*
* Minio Cloud Storage, (C) 2016, 2017 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 implements in memory caching methods.
package objcache
import (
"bytes"
"errors"
"io"
"runtime/debug"
"sync"
"time"
)
const (
// NoExpiry represents caches to be permanent and can only be deleted.
NoExpiry = time.Duration(0)
// DefaultExpiry represents three days time duration when individual entries will be expired.
DefaultExpiry = time.Duration(3 * 24 * time.Hour)
// defaultBufferRatio represents default ratio used to calculate the
// individual cache entry buffer size.
defaultBufferRatio = uint64(10)
// defaultGCPercent represents default garbage collection target percentage.
defaultGCPercent = 50
)
var (
// ErrKeyNotFoundInCache - key not found in cache.
ErrKeyNotFoundInCache = errors.New("Key not found in cache")
// ErrCacheFull - cache is full.
ErrCacheFull = errors.New("Not enough space in cache")
// ErrExcessData - excess data was attempted to be written on cache.
ErrExcessData = errors.New("Attempted excess write on cache")
)
// 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.Mutex
// Once is used for resetting GC once after
// peak cache usage.
onceGC sync.Once
// maxSize is a total size for overall cache
maxSize uint64
// maxCacheEntrySize is a total size per key buffer.
maxCacheEntrySize uint64
// currentSize is a current size in memory
currentSize uint64
// OnEviction - callback function for eviction
OnEviction func(key string)
// totalEvicted counter to keep track of total expirys
totalEvicted int
// map of objectName and its contents
entries map[string]*buffer
// Expiry in time duration.
expiry time.Duration
// Stop garbage collection routine, stops any running GC routine.
stopGC chan struct{}
}
// 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) (c *Cache, err error) {
if maxSize == 0 {
err = errors.New("invalid maximum cache size")
return c, err
}
// A garbage collection is triggered when the ratio
// of freshly allocated data to live data remaining
// after the previous collection reaches this percentage.
//
// - https://golang.org/pkg/runtime/debug/#SetGCPercent
//
// This means that by default GC is triggered after
// we've allocated an extra amount of memory proportional
// to the amount already in use.
//
// If gcpercent=100 and we're using 4M, we'll gc again
// when we get to 8M.
//
// Set this value to 40% if caching is enabled.
debug.SetGCPercent(defaultGCPercent)
// Max cache entry size - indicates the
// maximum buffer per key that can be held in
// memory. Currently this value is 1/10th
// the size of requested cache size.
maxCacheEntrySize := func() uint64 {
i := maxSize / defaultBufferRatio
if i == 0 {
i = maxSize
}
return i
}()
c = &Cache{
onceGC: sync.Once{},
maxSize: maxSize,
maxCacheEntrySize: maxCacheEntrySize,
entries: make(map[string]*buffer),
expiry: expiry,
}
// We have expiry start the janitor routine.
if expiry > 0 {
// Initialize a new stop GC channel.
c.stopGC = make(chan struct{})
// Start garbage collection routine to expire objects.
c.StartGC()
}
return c, nil
}
// 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) Create(key string, size int64) (w io.WriteCloser, err error) {
// 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)
// Check if the size of the object is > 1/10th the size
// of the cache, if yes then we ignore it.
if valueLen > c.maxCacheEntrySize {
return nil, ErrCacheFull
}
c.mutex.Lock()
// Check if the incoming size is going to exceed the
// effective cache size, if yes return error instead.
if c.currentSize+valueLen > c.maxSize {
c.mutex.Unlock()
return nil, ErrCacheFull
}
// Change GC percent if the current cache usage might
// become 75% of the maximum allowed usage, change
// the GC percent.
if c.currentSize+valueLen > (75 * c.maxSize / 100) {
c.onceGC.Do(func() { debug.SetGCPercent(defaultGCPercent - 25) })
}
c.mutex.Unlock()
cbuf := &cappedWriter{
offset: 0,
cap: size,
buffer: make([]byte, size),
}
// Function called on close which saves the object contents
// to the object cache.
onClose := func() error {
c.mutex.Lock()
defer c.mutex.Unlock()
if size != cbuf.offset {
cbuf.Reset() // Reset resets the buffer to be empty.
// Full object not available hence do not save buf to object cache.
return io.ErrShortBuffer
}
// Full object available in buf, save it to cache.
c.entries[key] = &buffer{
value: cbuf.buffer,
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 - cappedWriter.Write(data)
// will be accumulated in buf which implements io.Writer.
cbuf.onClose = onClose
// Capped writer.
return cbuf, nil
}
// Open - open the in-memory file, returns an in memory read seeker.
// returns an error ErrNotFoundInCache, if the key does not exist.
// Returns ErrKeyNotFoundInCache if entry's lastAccessedTime is older
// than objModTime.
func (c *Cache) Open(key string, objModTime time.Time) (io.ReaderAt, error) {
// Entry exists, return the readable buffer.
c.mutex.Lock()
defer c.mutex.Unlock()
buf, ok := c.entries[key]
if !ok {
return nil, ErrKeyNotFoundInCache
}
// Check if buf is recent copy of the object on disk.
if buf.lastAccessed.Before(objModTime) {
c.delete(key)
return nil, ErrKeyNotFoundInCache
}
buf.lastAccessed = time.Now().UTC()
return bytes.NewReader(buf.value), nil
}
// Delete - delete deletes an entry from the cache.
func (c *Cache) Delete(key string) {
c.mutex.Lock()
c.delete(key)
c.mutex.Unlock()
if c.OnEviction != nil {
c.OnEviction(key)
}
}
// 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, be careful if you are using this.
func (c *Cache) StopGC() {
if c.stopGC != nil {
c.stopGC <- struct{}{}
}
}
// 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 _, ok := c.entries[key]; ok {
deletedSize := uint64(len(c.entries[key].value))
delete(c.entries, key)
c.currentSize -= deletedSize
c.totalEvicted++
}
}

326
pkg/objcache/objcache_test.go
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@@ -1,326 +0,0 @@
/*
* 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"
"testing"
"time"
)
// TestObjectCache tests cases of object cache with expiry.
func TestObjExpiry(t *testing.T) {
// Non exhaustive list of all object cache behavior cases.
testCases := []struct {
expiry time.Duration
cacheSize uint64
err error
closeErr error
}{
{
expiry: 100 * time.Millisecond,
cacheSize: 1024,
err: ErrKeyNotFoundInCache,
closeErr: nil,
},
}
// Test case 1 validates running of GC.
testCase := testCases[0]
cache, err := New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
cache.OnEviction = func(key string) {}
w, err := cache.Create("test", 1)
if err != nil {
t.Errorf("Test case 1 expected to pass, failed instead %s", err)
}
// Write a byte.
w.Write([]byte("1"))
if err = w.Close(); err != nil {
t.Errorf("Test case 1 expected to pass, failed instead %s", err)
}
// Wait for 500 millisecond.
time.Sleep(500 * time.Millisecond)
// Setting objModTime to the beginning of golang's time.Time to avoid deletion of stale entry.
fakeObjModTime := time.Time{}
_, err = cache.Open("test", fakeObjModTime)
if err != testCase.err {
t.Errorf("Test case 1 expected %s, got instead %s", testCase.err, err)
}
}
// TestObjCache - tests various cases for object cache behavior.
func TestObjCache(t *testing.T) {
// Setting objModTime to the beginning of golang's time.Time to avoid deletion of stale entry.
fakeObjModTime := time.Time{}
// 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,
},
// Validate error excess data.
{
expiry: NoExpiry,
cacheSize: 5,
closeErr: ErrExcessData,
},
// Validate error excess data during write.
{
expiry: NoExpiry,
cacheSize: 2048,
err: ErrExcessData,
},
}
// Test 1 validating Open failure.
testCase := testCases[0]
cache, err := New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
_, err = cache.Open("test", fakeObjModTime)
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, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
_, 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, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
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, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
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", fakeObjModTime)
if err != nil {
t.Errorf("Test case 4 expected to pass, failed instead %s", err)
}
// Reads everything stored for key "test".
cbytes := make([]byte, 5)
_, err = r.ReadAt(cbytes, 0)
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, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
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", fakeObjModTime)
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, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
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)
}
// Test 7 validates rejecting requests when excess data is being saved.
testCase = testCases[6]
cache, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
w, err = cache.Create("test1", 5)
if err != nil {
t.Errorf("Test case 7 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 7 expected to pass, failed instead %s", err)
}
_, err = cache.Create("test2", 1)
if err != ErrCacheFull {
t.Errorf("Test case 7 expected to pass, failed instead %s", err)
}
// Test 8 validates rejecting Writes which write excess data.
testCase = testCases[7]
cache, err = New(testCase.cacheSize, testCase.expiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
w, err = cache.Create("test1", 5)
if err != nil {
t.Errorf("Test case 8 expected to pass, failed instead %s", err)
}
// Write '5' bytes.
n, err := w.Write([]byte("Hello"))
if err != nil {
t.Errorf("Test case 8 expected to pass, failed instead %s", err)
}
if n != 5 {
t.Errorf("Test case 8 expected 5 bytes written, instead found %d", n)
}
// Write '1' more byte, should return error.
n, err = w.Write([]byte("W"))
if n == 0 && err != testCase.err {
t.Errorf("Test case 8 expected to fail with ErrExcessData, but failed with %s instead", err)
}
}
// TestStateEntryPurge - tests if objCache purges stale entry and returns ErrKeyNotFoundInCache.
func TestStaleEntryPurge(t *testing.T) {
cache, err := New(1024, NoExpiry)
if err != nil {
t.Fatalf("Unable to create new objcache")
}
w, err := cache.Create("test", 5)
if err != nil {
t.Errorf("Test case 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 expected to pass, failed instead %s", err)
}
_, err = cache.Open("test", time.Now().AddDate(0, 0, 1).UTC())
if err != ErrKeyNotFoundInCache {
t.Errorf("Test case expected to return ErrKeyNotFoundInCache, instead returned %s", err)
}
}