392 lines
11 KiB
Go
392 lines
11 KiB
Go
package bbolt
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import (
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"fmt"
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"sort"
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"unsafe"
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)
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// txPending holds a list of pgids and corresponding allocation txns
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// that are pending to be freed.
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type txPending struct {
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ids []pgid
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alloctx []txid // txids allocating the ids
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lastReleaseBegin txid // beginning txid of last matching releaseRange
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}
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// pidSet holds the set of starting pgids which have the same span size
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type pidSet map[pgid]struct{}
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// freelist represents a list of all pages that are available for allocation.
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// It also tracks pages that have been freed but are still in use by open transactions.
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type freelist struct {
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freelistType FreelistType // freelist type
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ids []pgid // all free and available free page ids.
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allocs map[pgid]txid // mapping of txid that allocated a pgid.
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pending map[txid]*txPending // mapping of soon-to-be free page ids by tx.
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cache map[pgid]bool // fast lookup of all free and pending page ids.
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freemaps map[uint64]pidSet // key is the size of continuous pages(span), value is a set which contains the starting pgids of same size
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forwardMap map[pgid]uint64 // key is start pgid, value is its span size
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backwardMap map[pgid]uint64 // key is end pgid, value is its span size
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allocate func(txid txid, n int) pgid // the freelist allocate func
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free_count func() int // the function which gives you free page number
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mergeSpans func(ids pgids) // the mergeSpan func
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getFreePageIDs func() []pgid // get free pgids func
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readIDs func(pgids []pgid) // readIDs func reads list of pages and init the freelist
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}
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// newFreelist returns an empty, initialized freelist.
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func newFreelist(freelistType FreelistType) *freelist {
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f := &freelist{
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freelistType: freelistType,
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allocs: make(map[pgid]txid),
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pending: make(map[txid]*txPending),
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cache: make(map[pgid]bool),
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freemaps: make(map[uint64]pidSet),
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forwardMap: make(map[pgid]uint64),
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backwardMap: make(map[pgid]uint64),
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}
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if freelistType == FreelistMapType {
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f.allocate = f.hashmapAllocate
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f.free_count = f.hashmapFreeCount
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f.mergeSpans = f.hashmapMergeSpans
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f.getFreePageIDs = f.hashmapGetFreePageIDs
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f.readIDs = f.hashmapReadIDs
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} else {
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f.allocate = f.arrayAllocate
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f.free_count = f.arrayFreeCount
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f.mergeSpans = f.arrayMergeSpans
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f.getFreePageIDs = f.arrayGetFreePageIDs
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f.readIDs = f.arrayReadIDs
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}
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return f
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}
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// size returns the size of the page after serialization.
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func (f *freelist) size() int {
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n := f.count()
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if n >= 0xFFFF {
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// The first element will be used to store the count. See freelist.write.
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n++
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}
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return pageHeaderSize + (int(unsafe.Sizeof(pgid(0))) * n)
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}
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// count returns count of pages on the freelist
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func (f *freelist) count() int {
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return f.free_count() + f.pending_count()
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}
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// arrayFreeCount returns count of free pages(array version)
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func (f *freelist) arrayFreeCount() int {
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return len(f.ids)
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}
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// pending_count returns count of pending pages
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func (f *freelist) pending_count() int {
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var count int
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for _, txp := range f.pending {
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count += len(txp.ids)
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}
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return count
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}
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// copyall copies into dst a list of all free ids and all pending ids in one sorted list.
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// f.count returns the minimum length required for dst.
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func (f *freelist) copyall(dst []pgid) {
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m := make(pgids, 0, f.pending_count())
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for _, txp := range f.pending {
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m = append(m, txp.ids...)
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}
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sort.Sort(m)
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mergepgids(dst, f.getFreePageIDs(), m)
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}
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// arrayAllocate returns the starting page id of a contiguous list of pages of a given size.
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// If a contiguous block cannot be found then 0 is returned.
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func (f *freelist) arrayAllocate(txid txid, n int) pgid {
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if len(f.ids) == 0 {
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return 0
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}
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var initial, previd pgid
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for i, id := range f.ids {
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if id <= 1 {
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panic(fmt.Sprintf("invalid page allocation: %d", id))
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}
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// Reset initial page if this is not contiguous.
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if previd == 0 || id-previd != 1 {
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initial = id
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}
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// If we found a contiguous block then remove it and return it.
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if (id-initial)+1 == pgid(n) {
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// If we're allocating off the beginning then take the fast path
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// and just adjust the existing slice. This will use extra memory
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// temporarily but the append() in free() will realloc the slice
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// as is necessary.
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if (i + 1) == n {
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f.ids = f.ids[i+1:]
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} else {
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copy(f.ids[i-n+1:], f.ids[i+1:])
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f.ids = f.ids[:len(f.ids)-n]
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}
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// Remove from the free cache.
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for i := pgid(0); i < pgid(n); i++ {
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delete(f.cache, initial+i)
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}
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f.allocs[initial] = txid
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return initial
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}
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previd = id
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}
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return 0
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}
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// free releases a page and its overflow for a given transaction id.
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// If the page is already free then a panic will occur.
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func (f *freelist) free(txid txid, p *page) {
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if p.id <= 1 {
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panic(fmt.Sprintf("cannot free page 0 or 1: %d", p.id))
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}
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// Free page and all its overflow pages.
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txp := f.pending[txid]
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if txp == nil {
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txp = &txPending{}
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f.pending[txid] = txp
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}
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allocTxid, ok := f.allocs[p.id]
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if ok {
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delete(f.allocs, p.id)
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} else if (p.flags & freelistPageFlag) != 0 {
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// Freelist is always allocated by prior tx.
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allocTxid = txid - 1
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}
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for id := p.id; id <= p.id+pgid(p.overflow); id++ {
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// Verify that page is not already free.
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if f.cache[id] {
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panic(fmt.Sprintf("page %d already freed", id))
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}
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// Add to the freelist and cache.
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txp.ids = append(txp.ids, id)
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txp.alloctx = append(txp.alloctx, allocTxid)
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f.cache[id] = true
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}
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}
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// release moves all page ids for a transaction id (or older) to the freelist.
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func (f *freelist) release(txid txid) {
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m := make(pgids, 0)
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for tid, txp := range f.pending {
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if tid <= txid {
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// Move transaction's pending pages to the available freelist.
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// Don't remove from the cache since the page is still free.
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m = append(m, txp.ids...)
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delete(f.pending, tid)
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}
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}
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f.mergeSpans(m)
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}
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// releaseRange moves pending pages allocated within an extent [begin,end] to the free list.
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func (f *freelist) releaseRange(begin, end txid) {
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if begin > end {
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return
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}
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var m pgids
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for tid, txp := range f.pending {
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if tid < begin || tid > end {
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continue
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}
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// Don't recompute freed pages if ranges haven't updated.
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if txp.lastReleaseBegin == begin {
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continue
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}
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for i := 0; i < len(txp.ids); i++ {
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if atx := txp.alloctx[i]; atx < begin || atx > end {
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continue
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}
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m = append(m, txp.ids[i])
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txp.ids[i] = txp.ids[len(txp.ids)-1]
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txp.ids = txp.ids[:len(txp.ids)-1]
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txp.alloctx[i] = txp.alloctx[len(txp.alloctx)-1]
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txp.alloctx = txp.alloctx[:len(txp.alloctx)-1]
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i--
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}
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txp.lastReleaseBegin = begin
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if len(txp.ids) == 0 {
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delete(f.pending, tid)
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}
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}
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f.mergeSpans(m)
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}
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// rollback removes the pages from a given pending tx.
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func (f *freelist) rollback(txid txid) {
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// Remove page ids from cache.
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txp := f.pending[txid]
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if txp == nil {
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return
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}
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var m pgids
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for i, pgid := range txp.ids {
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delete(f.cache, pgid)
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tx := txp.alloctx[i]
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if tx == 0 {
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continue
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}
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if tx != txid {
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// Pending free aborted; restore page back to alloc list.
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f.allocs[pgid] = tx
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} else {
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// Freed page was allocated by this txn; OK to throw away.
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m = append(m, pgid)
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}
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}
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// Remove pages from pending list and mark as free if allocated by txid.
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delete(f.pending, txid)
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f.mergeSpans(m)
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}
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// freed returns whether a given page is in the free list.
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func (f *freelist) freed(pgid pgid) bool {
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return f.cache[pgid]
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}
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// read initializes the freelist from a freelist page.
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func (f *freelist) read(p *page) {
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if (p.flags & freelistPageFlag) == 0 {
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panic(fmt.Sprintf("invalid freelist page: %d, page type is %s", p.id, p.typ()))
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}
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// If the page.count is at the max uint16 value (64k) then it's considered
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// an overflow and the size of the freelist is stored as the first element.
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idx, count := 0, int(p.count)
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if count == 0xFFFF {
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idx = 1
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count = int(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0])
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}
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// Copy the list of page ids from the freelist.
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if count == 0 {
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f.ids = nil
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} else {
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ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[idx : idx+count]
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// copy the ids, so we don't modify on the freelist page directly
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idsCopy := make([]pgid, count)
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copy(idsCopy, ids)
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// Make sure they're sorted.
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sort.Sort(pgids(idsCopy))
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f.readIDs(idsCopy)
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}
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}
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// arrayReadIDs initializes the freelist from a given list of ids.
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func (f *freelist) arrayReadIDs(ids []pgid) {
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f.ids = ids
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f.reindex()
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}
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func (f *freelist) arrayGetFreePageIDs() []pgid {
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return f.ids
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}
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// write writes the page ids onto a freelist page. All free and pending ids are
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// saved to disk since in the event of a program crash, all pending ids will
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// become free.
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func (f *freelist) write(p *page) error {
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// Combine the old free pgids and pgids waiting on an open transaction.
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// Update the header flag.
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p.flags |= freelistPageFlag
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// The page.count can only hold up to 64k elements so if we overflow that
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// number then we handle it by putting the size in the first element.
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lenids := f.count()
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if lenids == 0 {
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p.count = uint16(lenids)
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} else if lenids < 0xFFFF {
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p.count = uint16(lenids)
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f.copyall(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:])
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} else {
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p.count = 0xFFFF
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((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0] = pgid(lenids)
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f.copyall(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[1:])
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}
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return nil
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}
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// reload reads the freelist from a page and filters out pending items.
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func (f *freelist) reload(p *page) {
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f.read(p)
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// Build a cache of only pending pages.
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pcache := make(map[pgid]bool)
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for _, txp := range f.pending {
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for _, pendingID := range txp.ids {
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pcache[pendingID] = true
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}
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}
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// Check each page in the freelist and build a new available freelist
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// with any pages not in the pending lists.
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var a []pgid
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for _, id := range f.getFreePageIDs() {
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if !pcache[id] {
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a = append(a, id)
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}
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}
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f.readIDs(a)
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}
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// noSyncReload reads the freelist from pgids and filters out pending items.
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func (f *freelist) noSyncReload(pgids []pgid) {
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// Build a cache of only pending pages.
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pcache := make(map[pgid]bool)
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for _, txp := range f.pending {
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for _, pendingID := range txp.ids {
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pcache[pendingID] = true
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}
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}
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// Check each page in the freelist and build a new available freelist
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// with any pages not in the pending lists.
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var a []pgid
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for _, id := range pgids {
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if !pcache[id] {
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a = append(a, id)
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}
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}
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f.readIDs(a)
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}
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// reindex rebuilds the free cache based on available and pending free lists.
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func (f *freelist) reindex() {
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ids := f.getFreePageIDs()
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f.cache = make(map[pgid]bool, len(ids))
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for _, id := range ids {
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f.cache[id] = true
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}
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for _, txp := range f.pending {
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for _, pendingID := range txp.ids {
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f.cache[pendingID] = true
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}
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}
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}
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// arrayMergeSpans try to merge list of pages(represented by pgids) with existing spans but using array
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func (f *freelist) arrayMergeSpans(ids pgids) {
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sort.Sort(ids)
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f.ids = pgids(f.ids).merge(ids)
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}
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