Add large bucket support for erasure coded backend (#5160)

This PR implements an object layer which
combines input erasure sets of XL layers
into a unified namespace.

This object layer extends the existing
erasure coded implementation, it is assumed
in this design that providing > 16 disks is
a static configuration as well i.e if you started
the setup with 32 disks with 4 sets 8 disks per
pack then you would need to provide 4 sets always.

Some design details and restrictions:

- Objects are distributed using consistent ordering
  to a unique erasure coded layer.
- Each pack has its own dsync so locks are synchronized
  properly at pack (erasure layer).
- Each pack still has a maximum of 16 disks
  requirement, you can start with multiple
  such sets statically.
- Static sets set of disks and cannot be
  changed, there is no elastic expansion allowed.
- Static sets set of disks and cannot be
  changed, there is no elastic removal allowed.
- ListObjects() across sets can be noticeably
  slower since List happens on all servers,
  and is merged at this sets layer.

Fixes #5465
Fixes #5464
Fixes #5461
Fixes #5460
Fixes #5459
Fixes #5458
Fixes #5460
Fixes #5488
Fixes #5489
Fixes #5497
Fixes #5496

pkg/bpool/bpool.go

@@ -0,0 +1,77 @@
+// Original work https://github.com/oxtoacart/bpool borrowed
+// only bpool.go licensed under Apache 2.0.
+
+// This file modifies original bpool.go to add one more option
+// to provide []byte capacity for better GC management.
+
+/*
+ * Minio Cloud Storage (C) 2018 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 bpool
+
+// BytePoolCap implements a leaky pool of []byte in the form of a bounded channel.
+type BytePoolCap struct {
+	c    chan []byte
+	w    int
+	wcap int
+}
+
+// NewBytePoolCap creates a new BytePool bounded to the given maxSize, with new
+// byte arrays sized based on width.
+func NewBytePoolCap(maxSize int, width int, capwidth int) (bp *BytePoolCap) {
+	return &BytePoolCap{
+		c:    make(chan []byte, maxSize),
+		w:    width,
+		wcap: capwidth,
+	}
+}
+
+// Get gets a []byte from the BytePool, or creates a new one if none are
+// available in the pool.
+func (bp *BytePoolCap) Get() (b []byte) {
+	select {
+	case b = <-bp.c:
+	// reuse existing buffer
+	default:
+		// create new buffer
+		if bp.wcap > 0 {
+			b = make([]byte, bp.w, bp.wcap)
+		} else {
+			b = make([]byte, bp.w)
+		}
+	}
+	return
+}
+
+// Put returns the given Buffer to the BytePool.
+func (bp *BytePoolCap) Put(b []byte) {
+	select {
+	case bp.c <- b:
+		// buffer went back into pool
+	default:
+		// buffer didn't go back into pool, just discard
+	}
+}
+
+// Width returns the width of the byte arrays in this pool.
+func (bp *BytePoolCap) Width() (n int) {
+	return bp.w
+}
+
+// WidthCap returns the cap width of the byte arrays in this pool.
+func (bp *BytePoolCap) WidthCap() (n int) {
+	return bp.wcap
+}