diff options
| -rw-r--r-- | db.go | 49 |
1 files changed, 38 insertions, 11 deletions
@@ -205,9 +205,15 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) { if _, err := db.file.ReadAt(buf[:], 0); err == nil { m := db.pageInBuffer(buf[:], 0).meta() if err := m.validate(); err != nil { - return nil, err + // If we can't read the page size, we can assume it's the same + // as the OS -- since that's how the page size was chosen in the + // first place. + // XXX: Does this cause issues with opening a database on a + // different OS than the one it was created on? + db.pageSize = os.Getpagesize() + } else { + db.pageSize = int(m.pageSize) } - db.pageSize = int(m.pageSize) } } @@ -274,12 +280,13 @@ func (db *DB) mmap(minsz int) error { db.meta0 = db.page(0).meta() db.meta1 = db.page(1).meta() - // Validate the meta pages. - if err := db.meta0.validate(); err != nil { - return err - } - if err := db.meta1.validate(); err != nil { - return err + // Validate the meta pages. We only return an error if both meta pages fail + // validation, since meta0 failing validation means that it wasn't saved + // properly -- but we can recover using meta1. And vice-versa. + err0 := db.meta0.validate() + err1 := db.meta1.validate() + if err0 != nil && err1 != nil { + return fmt.Errorf("meta0(%v) meta1(%v)", err0, err1) } return nil @@ -790,10 +797,30 @@ func (db *DB) pageInBuffer(b []byte, id pgid) *page { // meta retrieves the current meta page reference. func (db *DB) meta() *meta { - if db.meta0.txid > db.meta1.txid { - return db.meta0 + // We have to return the meta with the highest txid which doesn't fail + // validation. Otherwise, we can cause errors when in fact the database is + // in a consistent state. metaA is the one with the higher txid. + metaA := db.meta0 + metaB := db.meta1 + if db.meta1.txid > db.meta0.txid { + metaA = db.meta1 + metaB = db.meta0 } - return db.meta1 + + errA := metaA.validate() + errB := metaB.validate() + + if errA == nil { + return metaA + } + + if errB == nil { + return metaB + } + + // This should never be reached, because both meta1 and meta0 were validated + // on mmap() and we do fsync() on every write. + panic("both meta0 and meta1 could not be validated in DB.meta()!") } // allocate returns a contiguous block of memory starting at a given page. |