1package bolt 2 3import ( 4 "fmt" 5 "io" 6 "os" 7 "sort" 8 "strings" 9 "time" 10 "unsafe" 11) 12 13// txid represents the internal transaction identifier. 14type txid uint64 15 16// Tx represents a read-only or read/write transaction on the database. 17// Read-only transactions can be used for retrieving values for keys and creating cursors. 18// Read/write transactions can create and remove buckets and create and remove keys. 19// 20// IMPORTANT: You must commit or rollback transactions when you are done with 21// them. Pages can not be reclaimed by the writer until no more transactions 22// are using them. A long running read transaction can cause the database to 23// quickly grow. 24type Tx struct { 25 writable bool 26 managed bool 27 db *DB 28 meta *meta 29 root Bucket 30 pages map[pgid]*page 31 stats TxStats 32 commitHandlers []func() 33 34 // WriteFlag specifies the flag for write-related methods like WriteTo(). 35 // Tx opens the database file with the specified flag to copy the data. 36 // 37 // By default, the flag is unset, which works well for mostly in-memory 38 // workloads. For databases that are much larger than available RAM, 39 // set the flag to syscall.O_DIRECT to avoid trashing the page cache. 40 WriteFlag int 41} 42 43// init initializes the transaction. 44func (tx *Tx) init(db *DB) { 45 tx.db = db 46 tx.pages = nil 47 48 // Copy the meta page since it can be changed by the writer. 49 tx.meta = &meta{} 50 db.meta().copy(tx.meta) 51 52 // Copy over the root bucket. 53 tx.root = newBucket(tx) 54 tx.root.bucket = &bucket{} 55 *tx.root.bucket = tx.meta.root 56 57 // Increment the transaction id and add a page cache for writable transactions. 58 if tx.writable { 59 tx.pages = make(map[pgid]*page) 60 tx.meta.txid += txid(1) 61 } 62} 63 64// ID returns the transaction id. 65func (tx *Tx) ID() int { 66 return int(tx.meta.txid) 67} 68 69// DB returns a reference to the database that created the transaction. 70func (tx *Tx) DB() *DB { 71 return tx.db 72} 73 74// Size returns current database size in bytes as seen by this transaction. 75func (tx *Tx) Size() int64 { 76 return int64(tx.meta.pgid) * int64(tx.db.pageSize) 77} 78 79// Writable returns whether the transaction can perform write operations. 80func (tx *Tx) Writable() bool { 81 return tx.writable 82} 83 84// Cursor creates a cursor associated with the root bucket. 85// All items in the cursor will return a nil value because all root bucket keys point to buckets. 86// The cursor is only valid as long as the transaction is open. 87// Do not use a cursor after the transaction is closed. 88func (tx *Tx) Cursor() *Cursor { 89 return tx.root.Cursor() 90} 91 92// Stats retrieves a copy of the current transaction statistics. 93func (tx *Tx) Stats() TxStats { 94 return tx.stats 95} 96 97// Bucket retrieves a bucket by name. 98// Returns nil if the bucket does not exist. 99// The bucket instance is only valid for the lifetime of the transaction. 100func (tx *Tx) Bucket(name []byte) *Bucket { 101 return tx.root.Bucket(name) 102} 103 104// CreateBucket creates a new bucket. 105// Returns an error if the bucket already exists, if the bucket name is blank, or if the bucket name is too long. 106// The bucket instance is only valid for the lifetime of the transaction. 107func (tx *Tx) CreateBucket(name []byte) (*Bucket, error) { 108 return tx.root.CreateBucket(name) 109} 110 111// CreateBucketIfNotExists creates a new bucket if it doesn't already exist. 112// Returns an error if the bucket name is blank, or if the bucket name is too long. 113// The bucket instance is only valid for the lifetime of the transaction. 114func (tx *Tx) CreateBucketIfNotExists(name []byte) (*Bucket, error) { 115 return tx.root.CreateBucketIfNotExists(name) 116} 117 118// DeleteBucket deletes a bucket. 119// Returns an error if the bucket cannot be found or if the key represents a non-bucket value. 120func (tx *Tx) DeleteBucket(name []byte) error { 121 return tx.root.DeleteBucket(name) 122} 123 124// ForEach executes a function for each bucket in the root. 125// If the provided function returns an error then the iteration is stopped and 126// the error is returned to the caller. 127func (tx *Tx) ForEach(fn func(name []byte, b *Bucket) error) error { 128 return tx.root.ForEach(func(k, v []byte) error { 129 if err := fn(k, tx.root.Bucket(k)); err != nil { 130 return err 131 } 132 return nil 133 }) 134} 135 136// OnCommit adds a handler function to be executed after the transaction successfully commits. 137func (tx *Tx) OnCommit(fn func()) { 138 tx.commitHandlers = append(tx.commitHandlers, fn) 139} 140 141// Commit writes all changes to disk and updates the meta page. 142// Returns an error if a disk write error occurs, or if Commit is 143// called on a read-only transaction. 144func (tx *Tx) Commit() error { 145 _assert(!tx.managed, "managed tx commit not allowed") 146 if tx.db == nil { 147 return ErrTxClosed 148 } else if !tx.writable { 149 return ErrTxNotWritable 150 } 151 152 // TODO(benbjohnson): Use vectorized I/O to write out dirty pages. 153 154 // Rebalance nodes which have had deletions. 155 var startTime = time.Now() 156 tx.root.rebalance() 157 if tx.stats.Rebalance > 0 { 158 tx.stats.RebalanceTime += time.Since(startTime) 159 } 160 161 // spill data onto dirty pages. 162 startTime = time.Now() 163 if err := tx.root.spill(); err != nil { 164 tx.rollback() 165 return err 166 } 167 tx.stats.SpillTime += time.Since(startTime) 168 169 // Free the old root bucket. 170 tx.meta.root.root = tx.root.root 171 172 opgid := tx.meta.pgid 173 174 // Free the freelist and allocate new pages for it. This will overestimate 175 // the size of the freelist but not underestimate the size (which would be bad). 176 tx.db.freelist.free(tx.meta.txid, tx.db.page(tx.meta.freelist)) 177 p, err := tx.allocate((tx.db.freelist.size() / tx.db.pageSize) + 1) 178 if err != nil { 179 tx.rollback() 180 return err 181 } 182 if err := tx.db.freelist.write(p); err != nil { 183 tx.rollback() 184 return err 185 } 186 tx.meta.freelist = p.id 187 188 // If the high water mark has moved up then attempt to grow the database. 189 if tx.meta.pgid > opgid { 190 if err := tx.db.grow(int(tx.meta.pgid+1) * tx.db.pageSize); err != nil { 191 tx.rollback() 192 return err 193 } 194 } 195 196 // Write dirty pages to disk. 197 startTime = time.Now() 198 if err := tx.write(); err != nil { 199 tx.rollback() 200 return err 201 } 202 203 // If strict mode is enabled then perform a consistency check. 204 // Only the first consistency error is reported in the panic. 205 if tx.db.StrictMode { 206 ch := tx.Check() 207 var errs []string 208 for { 209 err, ok := <-ch 210 if !ok { 211 break 212 } 213 errs = append(errs, err.Error()) 214 } 215 if len(errs) > 0 { 216 panic("check fail: " + strings.Join(errs, "\n")) 217 } 218 } 219 220 // Write meta to disk. 221 if err := tx.writeMeta(); err != nil { 222 tx.rollback() 223 return err 224 } 225 tx.stats.WriteTime += time.Since(startTime) 226 227 // Finalize the transaction. 228 tx.close() 229 230 // Execute commit handlers now that the locks have been removed. 231 for _, fn := range tx.commitHandlers { 232 fn() 233 } 234 235 return nil 236} 237 238// Rollback closes the transaction and ignores all previous updates. Read-only 239// transactions must be rolled back and not committed. 240func (tx *Tx) Rollback() error { 241 _assert(!tx.managed, "managed tx rollback not allowed") 242 if tx.db == nil { 243 return ErrTxClosed 244 } 245 tx.rollback() 246 return nil 247} 248 249func (tx *Tx) rollback() { 250 if tx.db == nil { 251 return 252 } 253 if tx.writable { 254 tx.db.freelist.rollback(tx.meta.txid) 255 tx.db.freelist.reload(tx.db.page(tx.db.meta().freelist)) 256 } 257 tx.close() 258} 259 260func (tx *Tx) close() { 261 if tx.db == nil { 262 return 263 } 264 if tx.writable { 265 // Grab freelist stats. 266 var freelistFreeN = tx.db.freelist.free_count() 267 var freelistPendingN = tx.db.freelist.pending_count() 268 var freelistAlloc = tx.db.freelist.size() 269 270 // Remove transaction ref & writer lock. 271 tx.db.rwtx = nil 272 tx.db.rwlock.Unlock() 273 274 // Merge statistics. 275 tx.db.statlock.Lock() 276 tx.db.stats.FreePageN = freelistFreeN 277 tx.db.stats.PendingPageN = freelistPendingN 278 tx.db.stats.FreeAlloc = (freelistFreeN + freelistPendingN) * tx.db.pageSize 279 tx.db.stats.FreelistInuse = freelistAlloc 280 tx.db.stats.TxStats.add(&tx.stats) 281 tx.db.statlock.Unlock() 282 } else { 283 tx.db.removeTx(tx) 284 } 285 286 // Clear all references. 287 tx.db = nil 288 tx.meta = nil 289 tx.root = Bucket{tx: tx} 290 tx.pages = nil 291} 292 293// Copy writes the entire database to a writer. 294// This function exists for backwards compatibility. Use WriteTo() instead. 295func (tx *Tx) Copy(w io.Writer) error { 296 _, err := tx.WriteTo(w) 297 return err 298} 299 300// WriteTo writes the entire database to a writer. 301// If err == nil then exactly tx.Size() bytes will be written into the writer. 302func (tx *Tx) WriteTo(w io.Writer) (n int64, err error) { 303 // Attempt to open reader with WriteFlag 304 f, err := os.OpenFile(tx.db.path, os.O_RDONLY|tx.WriteFlag, 0) 305 if err != nil { 306 return 0, err 307 } 308 defer func() { _ = f.Close() }() 309 310 // Generate a meta page. We use the same page data for both meta pages. 311 buf := make([]byte, tx.db.pageSize) 312 page := (*page)(unsafe.Pointer(&buf[0])) 313 page.flags = metaPageFlag 314 *page.meta() = *tx.meta 315 316 // Write meta 0. 317 page.id = 0 318 page.meta().checksum = page.meta().sum64() 319 nn, err := w.Write(buf) 320 n += int64(nn) 321 if err != nil { 322 return n, fmt.Errorf("meta 0 copy: %s", err) 323 } 324 325 // Write meta 1 with a lower transaction id. 326 page.id = 1 327 page.meta().txid -= 1 328 page.meta().checksum = page.meta().sum64() 329 nn, err = w.Write(buf) 330 n += int64(nn) 331 if err != nil { 332 return n, fmt.Errorf("meta 1 copy: %s", err) 333 } 334 335 // Move past the meta pages in the file. 336 if _, err := f.Seek(int64(tx.db.pageSize*2), os.SEEK_SET); err != nil { 337 return n, fmt.Errorf("seek: %s", err) 338 } 339 340 // Copy data pages. 341 wn, err := io.CopyN(w, f, tx.Size()-int64(tx.db.pageSize*2)) 342 n += wn 343 if err != nil { 344 return n, err 345 } 346 347 return n, f.Close() 348} 349 350// CopyFile copies the entire database to file at the given path. 351// A reader transaction is maintained during the copy so it is safe to continue 352// using the database while a copy is in progress. 353func (tx *Tx) CopyFile(path string, mode os.FileMode) error { 354 f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, mode) 355 if err != nil { 356 return err 357 } 358 359 err = tx.Copy(f) 360 if err != nil { 361 _ = f.Close() 362 return err 363 } 364 return f.Close() 365} 366 367// Check performs several consistency checks on the database for this transaction. 368// An error is returned if any inconsistency is found. 369// 370// It can be safely run concurrently on a writable transaction. However, this 371// incurs a high cost for large databases and databases with a lot of subbuckets 372// because of caching. This overhead can be removed if running on a read-only 373// transaction, however, it is not safe to execute other writer transactions at 374// the same time. 375func (tx *Tx) Check() <-chan error { 376 ch := make(chan error) 377 go tx.check(ch) 378 return ch 379} 380 381func (tx *Tx) check(ch chan error) { 382 // Check if any pages are double freed. 383 freed := make(map[pgid]bool) 384 for _, id := range tx.db.freelist.all() { 385 if freed[id] { 386 ch <- fmt.Errorf("page %d: already freed", id) 387 } 388 freed[id] = true 389 } 390 391 // Track every reachable page. 392 reachable := make(map[pgid]*page) 393 reachable[0] = tx.page(0) // meta0 394 reachable[1] = tx.page(1) // meta1 395 for i := uint32(0); i <= tx.page(tx.meta.freelist).overflow; i++ { 396 reachable[tx.meta.freelist+pgid(i)] = tx.page(tx.meta.freelist) 397 } 398 399 // Recursively check buckets. 400 tx.checkBucket(&tx.root, reachable, freed, ch) 401 402 // Ensure all pages below high water mark are either reachable or freed. 403 for i := pgid(0); i < tx.meta.pgid; i++ { 404 _, isReachable := reachable[i] 405 if !isReachable && !freed[i] { 406 ch <- fmt.Errorf("page %d: unreachable unfreed", int(i)) 407 } 408 } 409 410 // Close the channel to signal completion. 411 close(ch) 412} 413 414func (tx *Tx) checkBucket(b *Bucket, reachable map[pgid]*page, freed map[pgid]bool, ch chan error) { 415 // Ignore inline buckets. 416 if b.root == 0 { 417 return 418 } 419 420 // Check every page used by this bucket. 421 b.tx.forEachPage(b.root, 0, func(p *page, _ int) { 422 if p.id > tx.meta.pgid { 423 ch <- fmt.Errorf("page %d: out of bounds: %d", int(p.id), int(b.tx.meta.pgid)) 424 } 425 426 // Ensure each page is only referenced once. 427 for i := pgid(0); i <= pgid(p.overflow); i++ { 428 var id = p.id + i 429 if _, ok := reachable[id]; ok { 430 ch <- fmt.Errorf("page %d: multiple references", int(id)) 431 } 432 reachable[id] = p 433 } 434 435 // We should only encounter un-freed leaf and branch pages. 436 if freed[p.id] { 437 ch <- fmt.Errorf("page %d: reachable freed", int(p.id)) 438 } else if (p.flags&branchPageFlag) == 0 && (p.flags&leafPageFlag) == 0 { 439 ch <- fmt.Errorf("page %d: invalid type: %s", int(p.id), p.typ()) 440 } 441 }) 442 443 // Check each bucket within this bucket. 444 _ = b.ForEach(func(k, v []byte) error { 445 if child := b.Bucket(k); child != nil { 446 tx.checkBucket(child, reachable, freed, ch) 447 } 448 return nil 449 }) 450} 451 452// allocate returns a contiguous block of memory starting at a given page. 453func (tx *Tx) allocate(count int) (*page, error) { 454 p, err := tx.db.allocate(count) 455 if err != nil { 456 return nil, err 457 } 458 459 // Save to our page cache. 460 tx.pages[p.id] = p 461 462 // Update statistics. 463 tx.stats.PageCount++ 464 tx.stats.PageAlloc += count * tx.db.pageSize 465 466 return p, nil 467} 468 469// write writes any dirty pages to disk. 470func (tx *Tx) write() error { 471 // Sort pages by id. 472 pages := make(pages, 0, len(tx.pages)) 473 for _, p := range tx.pages { 474 pages = append(pages, p) 475 } 476 // Clear out page cache early. 477 tx.pages = make(map[pgid]*page) 478 sort.Sort(pages) 479 480 // Write pages to disk in order. 481 for _, p := range pages { 482 size := (int(p.overflow) + 1) * tx.db.pageSize 483 offset := int64(p.id) * int64(tx.db.pageSize) 484 485 // Write out page in "max allocation" sized chunks. 486 ptr := (*[maxAllocSize]byte)(unsafe.Pointer(p)) 487 for { 488 // Limit our write to our max allocation size. 489 sz := size 490 if sz > maxAllocSize-1 { 491 sz = maxAllocSize - 1 492 } 493 494 // Write chunk to disk. 495 buf := ptr[:sz] 496 if _, err := tx.db.ops.writeAt(buf, offset); err != nil { 497 return err 498 } 499 500 // Update statistics. 501 tx.stats.Write++ 502 503 // Exit inner for loop if we've written all the chunks. 504 size -= sz 505 if size == 0 { 506 break 507 } 508 509 // Otherwise move offset forward and move pointer to next chunk. 510 offset += int64(sz) 511 ptr = (*[maxAllocSize]byte)(unsafe.Pointer(&ptr[sz])) 512 } 513 } 514 515 // Ignore file sync if flag is set on DB. 516 if !tx.db.NoSync || IgnoreNoSync { 517 if err := fdatasync(tx.db); err != nil { 518 return err 519 } 520 } 521 522 // Put small pages back to page pool. 523 for _, p := range pages { 524 // Ignore page sizes over 1 page. 525 // These are allocated using make() instead of the page pool. 526 if int(p.overflow) != 0 { 527 continue 528 } 529 530 buf := (*[maxAllocSize]byte)(unsafe.Pointer(p))[:tx.db.pageSize] 531 532 // See https://go.googlesource.com/go/+/f03c9202c43e0abb130669852082117ca50aa9b1 533 for i := range buf { 534 buf[i] = 0 535 } 536 tx.db.pagePool.Put(buf) 537 } 538 539 return nil 540} 541 542// writeMeta writes the meta to the disk. 543func (tx *Tx) writeMeta() error { 544 // Create a temporary buffer for the meta page. 545 buf := make([]byte, tx.db.pageSize) 546 p := tx.db.pageInBuffer(buf, 0) 547 tx.meta.write(p) 548 549 // Write the meta page to file. 550 if _, err := tx.db.ops.writeAt(buf, int64(p.id)*int64(tx.db.pageSize)); err != nil { 551 return err 552 } 553 if !tx.db.NoSync || IgnoreNoSync { 554 if err := fdatasync(tx.db); err != nil { 555 return err 556 } 557 } 558 559 // Update statistics. 560 tx.stats.Write++ 561 562 return nil 563} 564 565// page returns a reference to the page with a given id. 566// If page has been written to then a temporary buffered page is returned. 567func (tx *Tx) page(id pgid) *page { 568 // Check the dirty pages first. 569 if tx.pages != nil { 570 if p, ok := tx.pages[id]; ok { 571 return p 572 } 573 } 574 575 // Otherwise return directly from the mmap. 576 return tx.db.page(id) 577} 578 579// forEachPage iterates over every page within a given page and executes a function. 580func (tx *Tx) forEachPage(pgid pgid, depth int, fn func(*page, int)) { 581 p := tx.page(pgid) 582 583 // Execute function. 584 fn(p, depth) 585 586 // Recursively loop over children. 587 if (p.flags & branchPageFlag) != 0 { 588 for i := 0; i < int(p.count); i++ { 589 elem := p.branchPageElement(uint16(i)) 590 tx.forEachPage(elem.pgid, depth+1, fn) 591 } 592 } 593} 594 595// Page returns page information for a given page number. 596// This is only safe for concurrent use when used by a writable transaction. 597func (tx *Tx) Page(id int) (*PageInfo, error) { 598 if tx.db == nil { 599 return nil, ErrTxClosed 600 } else if pgid(id) >= tx.meta.pgid { 601 return nil, nil 602 } 603 604 // Build the page info. 605 p := tx.db.page(pgid(id)) 606 info := &PageInfo{ 607 ID: id, 608 Count: int(p.count), 609 OverflowCount: int(p.overflow), 610 } 611 612 // Determine the type (or if it's free). 613 if tx.db.freelist.freed(pgid(id)) { 614 info.Type = "free" 615 } else { 616 info.Type = p.typ() 617 } 618 619 return info, nil 620} 621 622// TxStats represents statistics about the actions performed by the transaction. 623type TxStats struct { 624 // Page statistics. 625 PageCount int // number of page allocations 626 PageAlloc int // total bytes allocated 627 628 // Cursor statistics. 629 CursorCount int // number of cursors created 630 631 // Node statistics 632 NodeCount int // number of node allocations 633 NodeDeref int // number of node dereferences 634 635 // Rebalance statistics. 636 Rebalance int // number of node rebalances 637 RebalanceTime time.Duration // total time spent rebalancing 638 639 // Split/Spill statistics. 640 Split int // number of nodes split 641 Spill int // number of nodes spilled 642 SpillTime time.Duration // total time spent spilling 643 644 // Write statistics. 645 Write int // number of writes performed 646 WriteTime time.Duration // total time spent writing to disk 647} 648 649func (s *TxStats) add(other *TxStats) { 650 s.PageCount += other.PageCount 651 s.PageAlloc += other.PageAlloc 652 s.CursorCount += other.CursorCount 653 s.NodeCount += other.NodeCount 654 s.NodeDeref += other.NodeDeref 655 s.Rebalance += other.Rebalance 656 s.RebalanceTime += other.RebalanceTime 657 s.Split += other.Split 658 s.Spill += other.Spill 659 s.SpillTime += other.SpillTime 660 s.Write += other.Write 661 s.WriteTime += other.WriteTime 662} 663 664// Sub calculates and returns the difference between two sets of transaction stats. 665// This is useful when obtaining stats at two different points and time and 666// you need the performance counters that occurred within that time span. 667func (s *TxStats) Sub(other *TxStats) TxStats { 668 var diff TxStats 669 diff.PageCount = s.PageCount - other.PageCount 670 diff.PageAlloc = s.PageAlloc - other.PageAlloc 671 diff.CursorCount = s.CursorCount - other.CursorCount 672 diff.NodeCount = s.NodeCount - other.NodeCount 673 diff.NodeDeref = s.NodeDeref - other.NodeDeref 674 diff.Rebalance = s.Rebalance - other.Rebalance 675 diff.RebalanceTime = s.RebalanceTime - other.RebalanceTime 676 diff.Split = s.Split - other.Split 677 diff.Spill = s.Spill - other.Spill 678 diff.SpillTime = s.SpillTime - other.SpillTime 679 diff.Write = s.Write - other.Write 680 diff.WriteTime = s.WriteTime - other.WriteTime 681 return diff 682} 683