voidDB/medium.go at master · figuerom16/voidDB · GitHub

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package voidDB

import (
	"github.com/voidDB/voidDB/common"
	"github.com/voidDB/voidDB/fifo"
)

type medium struct {
	*Txn

	keyspace []byte
}

func (txn medium) Meta() []byte {
	return common.TwinN(txn.meta, 1)
}

func (txn medium) Page(offset int) (page []byte, dirty bool) {
	return txn.Load(offset, common.PageSize)
}

func (txn medium) Data(offset, length int) (data []byte) {
	data, _ = txn.Load(offset, length)

	return
}

func (txn medium) Load(offset, length int) (data []byte, dirty bool) {
	data, dirty = txn.saveList[offset]

	if dirty {
		return
	}

	data = txn.read(offset, length)

	return
}

func (txn medium) Save(data []byte) (pointer int) {
	var (
		length int = align(
			len(data),
		)
	)

	pointer = txn.getFreePagePointer(length)

	txn.saveList[pointer] = data

	return
}

func (txn medium) Root(offset int) {
	txn.setRootNodePointer(txn.keyspace, offset)

	return
}

func (txn medium) SaveAt(offset int, data []byte) {
	txn.saveList[offset] = data

	return
}

func (txn medium) Free(offset, length int) {
	var (
		cool bool
	)

	length = align(length)

	switch _, cool = txn.saveList[offset]; cool {
	case true:
		txn.freeCool[length] = append(txn.freeCool[length], offset)

	default:
		txn.freeWarm[length] = append(txn.freeWarm[length], offset)
	}

	delete(txn.saveList, offset)

	return
}

func (txn medium) getFreePagePointer(size int) (pointer int) {
	var (
		e error
	)

	pointer = txn.getFreePageCool(size)

	if pointer > 0 {
		return
	}

	pointer, e = txn.getFreePageCold(size)

	if e != nil {
		pointer = txn.getFreePageNew(size)
	}

	return
}

func (txn medium) getFreePageCool(size int) (pointer int) {
	var (
		available bool
		pointers  []int
	)

	pointers, available = txn.freeCool[size]

	if !available {
		return -common.PageSize
	}

	pointer = pointers[0]

	txn.freeCool[size] = pointers[1:]

	if len(txn.freeCool[size]) == 0 {
		delete(txn.freeCool, size)
	}

	return
}

func (txn medium) getFreePageCold(size int) (pointer int, e error) {
	var (
		queue fifo.FIFO = txn.meta.freeQueue(size)
	)

	return queue.Dequeue(txn, txn.oldestReader)
}

func (txn medium) getFreePageNew(size int) (pointer int) {
	var (
		p int
	)

	pointer = txn.meta.getFrontierPointer()

	if size < common.PageSize {
		for p = pointer + size; p < pointer+common.PageSize; p += size {
			txn.freeCool[size] = append(txn.freeCool[size], p)
		}

		size = common.PageSize
	}

	txn.meta.setFrontierPointer(pointer + size)

	return
}

func align(size int) int {
	return 1 << logarithm(size)
}