diff options
Diffstat (limited to 'src/libstore')
| -rw-r--r-- | src/libstore/db.cc | 237 | ||||
| -rw-r--r-- | src/libstore/db.hh | 2 |
2 files changed, 133 insertions, 106 deletions
diff --git a/src/libstore/db.cc b/src/libstore/db.cc index 6740d6865..a0b1c16cd 100644 --- a/src/libstore/db.cc +++ b/src/libstore/db.cc @@ -165,127 +165,152 @@ static int my_fsync(int fd) } -void Database::open(const string & path) +void Database::open2(const string & path, bool removeOldEnv) { if (env) throw Error(format("environment already open")); - try { + debug(format("opening database environment")); + - debug(format("opening database environment")); - - - /* Create the database environment object. */ - DbEnv * env = 0; /* !!! close on error */ - env = new DbEnv(0); - - /* Smaller log files. */ - env->set_lg_bsize(32 * 1024); /* default */ - env->set_lg_max(256 * 1024); /* must be > 4 * lg_bsize */ - - /* Write the log, but don't sync. This protects transactions - against application crashes, but if the system crashes, - some transactions may be undone. An acceptable risk, I - think. */ - env->set_flags(DB_TXN_WRITE_NOSYNC | DB_LOG_AUTOREMOVE, 1); - - /* Increase the locking limits. If you ever get `Dbc::get: - Cannot allocate memory' or similar, especially while - running `nix-store --verify', just increase the following - number, then run db_recover on the database to remove the - existing DB environment (since changes only take effect on - new environments). */ - env->set_lk_max_locks(10000); - env->set_lk_max_lockers(10000); - env->set_lk_max_objects(10000); - env->set_lk_detect(DB_LOCK_DEFAULT); - - /* Dangerous, probably, but from the docs it *seems* that BDB - shouldn't sync when DB_TXN_WRITE_NOSYNC is used, but it - still fsync()s sometimes. */ - db_env_set_func_fsync(my_fsync); + /* Create the database environment object. */ + DbEnv * env = 0; /* !!! close on error */ + env = new DbEnv(0); + + /* Smaller log files. */ + env->set_lg_bsize(32 * 1024); /* default */ + env->set_lg_max(256 * 1024); /* must be > 4 * lg_bsize */ + + /* Write the log, but don't sync. This protects transactions + against application crashes, but if the system crashes, some + transactions may be undone. An acceptable risk, I think. */ + env->set_flags(DB_TXN_WRITE_NOSYNC | DB_LOG_AUTOREMOVE, 1); + + /* Increase the locking limits. If you ever get `Dbc::get: Cannot + allocate memory' or similar, especially while running + `nix-store --verify', just increase the following number, then + run db_recover on the database to remove the existing DB + environment (since changes only take effect on new + environments). */ + env->set_lk_max_locks(10000); + env->set_lk_max_lockers(10000); + env->set_lk_max_objects(10000); + env->set_lk_detect(DB_LOCK_DEFAULT); + + /* Dangerous, probably, but from the docs it *seems* that BDB + shouldn't sync when DB_TXN_WRITE_NOSYNC is used, but it still + fsync()s sometimes. */ + db_env_set_func_fsync(my_fsync); - /* The following code provides automatic recovery of the - database environment. Recovery is necessary when a process - dies while it has the database open. To detect this, - processes atomically increment a counter when they open the - database, and decrement it when they close it. If we see - that counter is > 0 but no processes are accessing the - database---determined by attempting to obtain a write lock - on a lock file on which all accessors have a read lock---we - must run recovery. Note that this also ensures that we - only run recovery when there are no other accessors (which - could cause database corruption). */ - - /* !!! close fdAccessors / fdLock on exception */ - - /* Open the accessor count file. */ - string accessorsPath = path + "/accessor_count"; - fdAccessors = ::open(accessorsPath.c_str(), O_RDWR | O_CREAT, 0666); - if (fdAccessors == -1) - if (errno == EACCES) - throw DbNoPermission( - format("permission denied to database in `%1%'") % accessorsPath); - else - throw SysError(format("opening file `%1%'") % accessorsPath); - - /* Open the lock file. */ - string lockPath = path + "/access_lock"; - fdLock = ::open(lockPath.c_str(), O_RDWR | O_CREAT, 0666); - if (fdLock == -1) - throw SysError(format("opening lock file `%1%'") % lockPath); - - /* Try to acquire a write lock. */ - debug(format("attempting write lock on `%1%'") % lockPath); - if (lockFile(fdLock, ltWrite, false)) { /* don't wait */ - - debug(format("write lock granted")); - - /* We have a write lock, which means that there are no - other readers or writers. */ - - int n = getAccessorCount(fdAccessors); - - if (n != 0) { - printMsg(lvlTalkative, - format("accessor count is %1%, running recovery") % n); - - /* Open the environment after running recovery. */ - openEnv(env, path, DB_RECOVER); - } + /* The following code provides automatic recovery of the database + environment. Recovery is necessary when a process dies while + it has the database open. To detect this, processes atomically + increment a counter when they open the database, and decrement + it when they close it. If we see that counter is > 0 but no + processes are accessing the database---determined by attempting + to obtain a write lock on a lock file on which all accessors + have a read lock---we must run recovery. Note that this also + ensures that we only run recovery when there are no other + accessors (which could cause database corruption). */ + + /* !!! close fdAccessors / fdLock on exception */ + + /* Open the accessor count file. */ + string accessorsPath = path + "/accessor_count"; + fdAccessors = ::open(accessorsPath.c_str(), O_RDWR | O_CREAT, 0666); + if (fdAccessors == -1) + if (errno == EACCES) + throw DbNoPermission( + format("permission denied to database in `%1%'") % accessorsPath); + else + throw SysError(format("opening file `%1%'") % accessorsPath); + + /* Open the lock file. */ + string lockPath = path + "/access_lock"; + fdLock = ::open(lockPath.c_str(), O_RDWR | O_CREAT, 0666); + if (fdLock == -1) + throw SysError(format("opening lock file `%1%'") % lockPath); + + /* Try to acquire a write lock. */ + debug(format("attempting write lock on `%1%'") % lockPath); + if (lockFile(fdLock, ltWrite, false)) { /* don't wait */ + + debug(format("write lock granted")); + + /* We have a write lock, which means that there are no other + readers or writers. */ + + if (removeOldEnv) { + printMsg(lvlError, "removing old Berkeley DB database environment..."); + env->remove(path.c_str(), DB_FORCE); + return; + } + + int n = getAccessorCount(fdAccessors); + + if (n != 0) { + printMsg(lvlTalkative, + format("accessor count is %1%, running recovery") % n); + + /* Open the environment after running recovery. */ + openEnv(env, path, DB_RECOVER); + } - else - /* Open the environment normally. */ - openEnv(env, path, 0); + else + /* Open the environment normally. */ + openEnv(env, path, 0); - setAccessorCount(fdAccessors, 1); + setAccessorCount(fdAccessors, 1); - /* Downgrade to a read lock. */ - debug(format("downgrading to read lock on `%1%'") % lockPath); - lockFile(fdLock, ltRead, true); + /* Downgrade to a read lock. */ + debug(format("downgrading to read lock on `%1%'") % lockPath); + lockFile(fdLock, ltRead, true); - } else { - /* There are other accessors. */ - debug(format("write lock refused")); + } else { + /* There are other accessors. */ + debug(format("write lock refused")); - /* Acquire a read lock. */ - debug(format("acquiring read lock on `%1%'") % lockPath); - lockFile(fdLock, ltRead, true); /* wait indefinitely */ + /* Acquire a read lock. */ + debug(format("acquiring read lock on `%1%'") % lockPath); + lockFile(fdLock, ltRead, true); /* wait indefinitely */ + + /* Increment the accessor count. */ + lockFile(fdAccessors, ltWrite, true); + int n = getAccessorCount(fdAccessors) + 1; + setAccessorCount(fdAccessors, n); + debug(format("incremented accessor count to %1%") % n); + lockFile(fdAccessors, ltNone, true); + + /* Open the environment normally. */ + openEnv(env, path, 0); + } + + this->env = env; +} - /* Increment the accessor count. */ - lockFile(fdAccessors, ltWrite, true); - int n = getAccessorCount(fdAccessors) + 1; - setAccessorCount(fdAccessors, n); - debug(format("incremented accessor count to %1%") % n); - lockFile(fdAccessors, ltNone, true); - /* Open the environment normally. */ - openEnv(env, path, 0); - } +void Database::open(const string & path) +{ + try { - this->env = env; + open2(path, false); - } catch (DbException e) { rethrow(e); } + } catch (DbException e) { + + if (e.get_errno() == DB_VERSION_MISMATCH) { + /* Remove the environment while we are holding the global + lock. If things go wrong there, we bail out. !!! + there is some leakage here op DbEnv and lock + handles. */ + open2(path, true); + + /* Try again. */ + open2(path, false); + } + else + rethrow(e); + } + } diff --git a/src/libstore/db.hh b/src/libstore/db.hh index 841836492..b962d77bc 100644 --- a/src/libstore/db.hh +++ b/src/libstore/db.hh @@ -58,6 +58,8 @@ private: Db * getDb(TableId table); + void open2(const string & path, bool removeOldEnv); + public: Database(); ~Database(); |