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memory.go
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memory.go
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// Copyright 2020-2021 Dolthub, 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 sql
import (
"os"
"runtime"
"strconv"
"sync"
errors "gopkg.in/src-d/go-errors.v1"
)
// Disposable objects can erase all their content when they're no longer in use.
// Expressions and Nodes that implement Disposable will have Dispose called on them as a final stage of query
// execution. This can be used to clean up cached memory that wouldn't get caught via the normal garbage collection
// process.
type Disposable interface {
// Dispose the contents.
Dispose()
}
func Dispose(i interface{}) {
if d, ok := i.(Disposable); ok {
d.Dispose()
}
}
// Freeable objects can free their memory.
type Freeable interface {
// Free the memory.
Free()
}
// KeyValueCache is a cache of key value pairs.
type KeyValueCache interface {
// Put a new value in the cache.
Put(uint64, interface{}) error
// Get the value with the given key.
Get(uint64) (interface{}, error)
// Size returns the number of elements in the cache.
Size() int
}
// RowsCache is a cache of rows.
type RowsCache interface {
// Add a new row to the cache. If there is no memory available, it will try to
// free some memory. If after that there is still no memory available, it
// will return an error and erase all the content of the cache.
Add(Row) error
// Get all rows.
Get() []Row
}
// ErrNoMemoryAvailable is returned when there is no more available memory.
var ErrNoMemoryAvailable = errors.NewKind("no memory available")
const maxMemoryKey = "MAX_MEMORY"
const (
b = 1
kib = 1024 * b
mib = 1024 * kib
)
var maxMemory = func() uint64 {
val := os.Getenv(maxMemoryKey)
var v uint64
if val != "" {
var err error
v, err = strconv.ParseUint(val, 10, 64)
if err != nil {
panic("MAX_MEMORY environment variable must be a number, but got: " + val)
}
}
return v * uint64(mib)
}()
// Reporter is a component that gives information about the memory usage.
type Reporter interface {
// MaxMemory returns the maximum number of memory allowed in bytes.
MaxMemory() uint64
// UsedMemory returns the memory in use in bytes.
UsedMemory() uint64
}
// ProcessMemory is a reporter for the memory used by the process and the
// maximum amount of memory allowed controlled by the MAX_MEMORY environment
// variable.
var ProcessMemory Reporter = new(processReporter)
type processReporter struct{}
func (processReporter) UsedMemory() uint64 {
var s runtime.MemStats
runtime.ReadMemStats(&s)
return s.HeapInuse + s.StackInuse
}
func (processReporter) MaxMemory() uint64 { return maxMemory }
// HasAvailableMemory reports whether more memory is available to the program if
// it hasn't reached the max memory limit.
func HasAvailableMemory(r Reporter) bool {
maxMemory := r.MaxMemory()
if maxMemory == 0 {
return true
}
return r.UsedMemory() < maxMemory
}
// MemoryManager is in charge of keeping track and managing all the components that operate
// in memory. There should only be one instance of a memory manager running at the
// same time in each process.
type MemoryManager struct {
mu sync.RWMutex
reporter Reporter
caches map[uint64]Disposable
token uint64
}
// NewMemoryManager creates a new manager with the given memory reporter. If nil is given,
// then the Process reporter will be used by default.
func NewMemoryManager(r Reporter) *MemoryManager {
if r == nil {
r = ProcessMemory
}
return &MemoryManager{
reporter: r,
caches: make(map[uint64]Disposable),
}
}
// HasAvailable reports whether the memory manager has any available memory.
func (m *MemoryManager) HasAvailable() bool {
return HasAvailableMemory(m.reporter)
}
// DisposeFunc is a function to completely erase a cache and remove it from the manager.
type DisposeFunc func()
// NewLRUCache returns an empty LRU cache and a function to dispose it when it's
// no longer needed.
func (m *MemoryManager) NewLRUCache(size uint) (KeyValueCache, DisposeFunc) {
c := newLRUCache(m, m.reporter, size)
pos := m.addCache(c)
return c, func() {
c.Dispose()
m.removeCache(pos)
}
}
// NewHistoryCache returns an empty history cache and a function to dispose it when it's
// no longer needed.
func (m *MemoryManager) NewHistoryCache() (KeyValueCache, DisposeFunc) {
c := newHistoryCache(m, m.reporter)
pos := m.addCache(c)
return c, func() {
c.Dispose()
m.removeCache(pos)
}
}
// NewRowsCache returns an empty rows cache and a function to dispose it when it's
// no longer needed.
func (m *MemoryManager) NewRowsCache() (RowsCache, DisposeFunc) {
c := newRowsCache(m, m.reporter)
pos := m.addCache(c)
return c, func() {
c.Dispose()
m.removeCache(pos)
}
}
func (m *MemoryManager) addCache(c Disposable) (pos uint64) {
m.mu.Lock()
defer m.mu.Unlock()
m.token++
m.caches[m.token] = c
return m.token
}
func (m *MemoryManager) removeCache(pos uint64) {
m.mu.Lock()
defer m.mu.Unlock()
delete(m.caches, pos)
if len(m.caches) == 0 {
m.token = 0
}
}
// Free the memory of all freeable caches.
func (m *MemoryManager) Free() {
m.mu.RLock()
defer m.mu.RUnlock()
for _, c := range m.caches {
if f, ok := c.(Freeable); ok {
f.Free()
}
}
}
func (m *MemoryManager) NumCaches() int {
m.mu.RLock()
defer m.mu.RUnlock()
return len(m.caches)
}