diff options
Diffstat (limited to 'db.go')
| -rw-r--r-- | db.go | 61 |
1 files changed, 51 insertions, 10 deletions
@@ -104,6 +104,10 @@ type DB struct { ops struct { writeAt func(b []byte, off int64) (n int, err error) } + + // Read only mode. + // When true, Update() and Begin(true) return ErrDatabaseReadOnly immediately. + readOnly bool } // Path returns the path to currently open database file. @@ -137,19 +141,28 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) { db.MaxBatchSize = DefaultMaxBatchSize db.MaxBatchDelay = DefaultMaxBatchDelay + flag := os.O_RDWR + if options.ReadOnly { + flag = os.O_RDONLY + db.readOnly = true + } + // Open data file and separate sync handler for metadata writes. db.path = path - var err error - if db.file, err = os.OpenFile(db.path, os.O_RDWR|os.O_CREATE, mode); err != nil { + if db.file, err = os.OpenFile(db.path, flag|os.O_CREATE, mode); err != nil { _ = db.close() return nil, err } - // Lock file so that other processes using Bolt cannot use the database - // at the same time. This would cause corruption since the two processes - // would write meta pages and free pages separately. - if err := flock(db.file, options.Timeout); err != nil { + // Lock file so that other processes using Bolt in read-write mode cannot + // use the database at the same time. This would cause corruption since + // the two processes would write meta pages and free pages separately. + // The database file is locked exclusively (only one process can grab the lock) + // if !options.ReadOnly. + // The database file is locked using the shared lock (more than one process may + // hold a lock at the same time) otherwise (options.ReadOnly is set). + if err := flock(db.file, !db.readOnly, options.Timeout); err != nil { _ = db.close() return nil, err } @@ -256,8 +269,8 @@ func (db *DB) munmap() error { // of the database. The minimum size is 1MB and doubles until it reaches 1GB. // Returns an error if the new mmap size is greater than the max allowed. func (db *DB) mmapSize(size int) (int, error) { - // Double the size from 1MB until 1GB. - for i := uint(20); i <= 30; i++ { + // Double the size from 32KB until 1GB. + for i := uint(15); i <= 30; i++ { if size <= 1<<i { return 1 << i, nil } @@ -338,8 +351,15 @@ func (db *DB) init() error { // Close releases all database resources. // All transactions must be closed before closing the database. func (db *DB) Close() error { + db.rwlock.Lock() + defer db.rwlock.Unlock() + db.metalock.Lock() defer db.metalock.Unlock() + + db.mmaplock.RLock() + defer db.mmaplock.RUnlock() + return db.close() } @@ -359,8 +379,11 @@ func (db *DB) close() error { // Close file handles. if db.file != nil { - // Unlock the file. - _ = funlock(db.file) + // No need to unlock read-only file. + if !db.readOnly { + // Unlock the file. + _ = funlock(db.file) + } // Close the file descriptor. if err := db.file.Close(); err != nil { @@ -378,6 +401,11 @@ func (db *DB) close() error { // will cause the calls to block and be serialized until the current write // transaction finishes. // +// Transactions should not be depedent on one another. Opening a read +// transaction and a write transaction in the same goroutine can cause the +// writer to deadlock because the database periodically needs to re-mmap itself +// as it grows and it cannot do that while a read transaction is open. +// // IMPORTANT: You must close read-only transactions after you are finished or // else the database will not reclaim old pages. func (db *DB) Begin(writable bool) (*Tx, error) { @@ -426,6 +454,11 @@ func (db *DB) beginTx() (*Tx, error) { } func (db *DB) beginRWTx() (*Tx, error) { + // If the database was opened with Options.ReadOnly, return an error. + if db.readOnly { + return nil, ErrDatabaseReadOnly + } + // Obtain writer lock. This is released by the transaction when it closes. // This enforces only one writer transaction at a time. db.rwlock.Lock() @@ -622,6 +655,10 @@ func (db *DB) allocate(count int) (*page, error) { return p, nil } +func (db *DB) IsReadOnly() bool { + return db.readOnly +} + // Options represents the options that can be set when opening a database. type Options struct { // Timeout is the amount of time to wait to obtain a file lock. @@ -631,6 +668,10 @@ type Options struct { // Sets the DB.NoGrowSync flag before memory mapping the file. NoGrowSync bool + + // Open database in read-only mode. Uses flock(..., LOCK_SH |LOCK_NB) to + // grab a shared lock (UNIX). + ReadOnly bool } // DefaultOptions represent the options used if nil options are passed into Open(). |