* Automatically upgrade the Berkeley DB environment if necessary.
This commit is contained in:
Eelco Dolstra
parent
88dea78cdf
commit
8f57634c14
2 changed files with 134 additions and 107 deletions
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@ -165,127 +165,152 @@ static int my_fsync(int fd)
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}
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void Database::open(const string & path)
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void Database::open2(const string & path, bool removeOldEnv)
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{
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if (env) throw Error(format("environment already open"));
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try {
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debug(format("opening database environment"));
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debug(format("opening database environment"));
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/* Create the database environment object. */
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DbEnv * env = 0; /* !!! close on error */
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env = new DbEnv(0);
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/* Smaller log files. */
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env->set_lg_bsize(32 * 1024); /* default */
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env->set_lg_max(256 * 1024); /* must be > 4 * lg_bsize */
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/* Write the log, but don't sync. This protects transactions
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against application crashes, but if the system crashes,
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some transactions may be undone. An acceptable risk, I
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think. */
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env->set_flags(DB_TXN_WRITE_NOSYNC | DB_LOG_AUTOREMOVE, 1);
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/* Increase the locking limits. If you ever get `Dbc::get:
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Cannot allocate memory' or similar, especially while
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running `nix-store --verify', just increase the following
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number, then run db_recover on the database to remove the
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existing DB environment (since changes only take effect on
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new environments). */
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env->set_lk_max_locks(10000);
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env->set_lk_max_lockers(10000);
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env->set_lk_max_objects(10000);
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env->set_lk_detect(DB_LOCK_DEFAULT);
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/* Dangerous, probably, but from the docs it *seems* that BDB
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shouldn't sync when DB_TXN_WRITE_NOSYNC is used, but it
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still fsync()s sometimes. */
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db_env_set_func_fsync(my_fsync);
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/* Create the database environment object. */
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DbEnv * env = 0; /* !!! close on error */
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env = new DbEnv(0);
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/* Smaller log files. */
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env->set_lg_bsize(32 * 1024); /* default */
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env->set_lg_max(256 * 1024); /* must be > 4 * lg_bsize */
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/* Write the log, but don't sync. This protects transactions
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against application crashes, but if the system crashes, some
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transactions may be undone. An acceptable risk, I think. */
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env->set_flags(DB_TXN_WRITE_NOSYNC | DB_LOG_AUTOREMOVE, 1);
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/* Increase the locking limits. If you ever get `Dbc::get: Cannot
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allocate memory' or similar, especially while running
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`nix-store --verify', just increase the following number, then
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run db_recover on the database to remove the existing DB
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environment (since changes only take effect on new
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environments). */
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env->set_lk_max_locks(10000);
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env->set_lk_max_lockers(10000);
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env->set_lk_max_objects(10000);
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env->set_lk_detect(DB_LOCK_DEFAULT);
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/* Dangerous, probably, but from the docs it *seems* that BDB
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shouldn't sync when DB_TXN_WRITE_NOSYNC is used, but it still
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fsync()s sometimes. */
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db_env_set_func_fsync(my_fsync);
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/* The following code provides automatic recovery of the
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database environment. Recovery is necessary when a process
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dies while it has the database open. To detect this,
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processes atomically increment a counter when they open the
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database, and decrement it when they close it. If we see
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that counter is > 0 but no processes are accessing the
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database---determined by attempting to obtain a write lock
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on a lock file on which all accessors have a read lock---we
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must run recovery. Note that this also ensures that we
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only run recovery when there are no other accessors (which
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could cause database corruption). */
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/* The following code provides automatic recovery of the database
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environment. Recovery is necessary when a process dies while
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it has the database open. To detect this, processes atomically
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increment a counter when they open the database, and decrement
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it when they close it. If we see that counter is > 0 but no
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processes are accessing the database---determined by attempting
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to obtain a write lock on a lock file on which all accessors
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have a read lock---we must run recovery. Note that this also
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ensures that we only run recovery when there are no other
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accessors (which could cause database corruption). */
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/* !!! close fdAccessors / fdLock on exception */
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/* !!! close fdAccessors / fdLock on exception */
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/* Open the accessor count file. */
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string accessorsPath = path + "/accessor_count";
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fdAccessors = ::open(accessorsPath.c_str(), O_RDWR | O_CREAT, 0666);
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if (fdAccessors == -1)
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if (errno == EACCES)
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throw DbNoPermission(
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format("permission denied to database in `%1%'") % accessorsPath);
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else
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throw SysError(format("opening file `%1%'") % accessorsPath);
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/* Open the lock file. */
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string lockPath = path + "/access_lock";
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fdLock = ::open(lockPath.c_str(), O_RDWR | O_CREAT, 0666);
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if (fdLock == -1)
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throw SysError(format("opening lock file `%1%'") % lockPath);
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/* Try to acquire a write lock. */
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debug(format("attempting write lock on `%1%'") % lockPath);
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if (lockFile(fdLock, ltWrite, false)) { /* don't wait */
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debug(format("write lock granted"));
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/* We have a write lock, which means that there are no
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other readers or writers. */
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int n = getAccessorCount(fdAccessors);
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if (n != 0) {
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printMsg(lvlTalkative,
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format("accessor count is %1%, running recovery") % n);
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/* Open the environment after running recovery. */
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openEnv(env, path, DB_RECOVER);
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}
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/* Open the accessor count file. */
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string accessorsPath = path + "/accessor_count";
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fdAccessors = ::open(accessorsPath.c_str(), O_RDWR | O_CREAT, 0666);
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if (fdAccessors == -1)
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if (errno == EACCES)
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throw DbNoPermission(
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format("permission denied to database in `%1%'") % accessorsPath);
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else
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throw SysError(format("opening file `%1%'") % accessorsPath);
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/* Open the lock file. */
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string lockPath = path + "/access_lock";
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fdLock = ::open(lockPath.c_str(), O_RDWR | O_CREAT, 0666);
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if (fdLock == -1)
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throw SysError(format("opening lock file `%1%'") % lockPath);
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/* Try to acquire a write lock. */
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debug(format("attempting write lock on `%1%'") % lockPath);
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if (lockFile(fdLock, ltWrite, false)) { /* don't wait */
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debug(format("write lock granted"));
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/* We have a write lock, which means that there are no other
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readers or writers. */
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if (removeOldEnv) {
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printMsg(lvlError, "removing old Berkeley DB database environment...");
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env->remove(path.c_str(), DB_FORCE);
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return;
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}
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int n = getAccessorCount(fdAccessors);
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if (n != 0) {
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printMsg(lvlTalkative,
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format("accessor count is %1%, running recovery") % n);
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else
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/* Open the environment normally. */
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openEnv(env, path, 0);
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setAccessorCount(fdAccessors, 1);
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/* Downgrade to a read lock. */
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debug(format("downgrading to read lock on `%1%'") % lockPath);
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lockFile(fdLock, ltRead, true);
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} else {
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/* There are other accessors. */
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debug(format("write lock refused"));
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/* Acquire a read lock. */
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debug(format("acquiring read lock on `%1%'") % lockPath);
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lockFile(fdLock, ltRead, true); /* wait indefinitely */
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/* Increment the accessor count. */
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lockFile(fdAccessors, ltWrite, true);
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int n = getAccessorCount(fdAccessors) + 1;
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setAccessorCount(fdAccessors, n);
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debug(format("incremented accessor count to %1%") % n);
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lockFile(fdAccessors, ltNone, true);
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/* Open the environment after running recovery. */
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openEnv(env, path, DB_RECOVER);
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}
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else
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/* Open the environment normally. */
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openEnv(env, path, 0);
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}
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this->env = env;
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setAccessorCount(fdAccessors, 1);
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/* Downgrade to a read lock. */
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debug(format("downgrading to read lock on `%1%'") % lockPath);
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lockFile(fdLock, ltRead, true);
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} else {
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/* There are other accessors. */
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debug(format("write lock refused"));
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/* Acquire a read lock. */
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debug(format("acquiring read lock on `%1%'") % lockPath);
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lockFile(fdLock, ltRead, true); /* wait indefinitely */
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} catch (DbException e) { rethrow(e); }
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/* Increment the accessor count. */
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lockFile(fdAccessors, ltWrite, true);
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int n = getAccessorCount(fdAccessors) + 1;
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setAccessorCount(fdAccessors, n);
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debug(format("incremented accessor count to %1%") % n);
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lockFile(fdAccessors, ltNone, true);
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/* Open the environment normally. */
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openEnv(env, path, 0);
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}
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this->env = env;
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}
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void Database::open(const string & path)
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{
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try {
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open2(path, false);
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} catch (DbException e) {
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if (e.get_errno() == DB_VERSION_MISMATCH) {
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/* Remove the environment while we are holding the global
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lock. If things go wrong there, we bail out. !!!
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there is some leakage here op DbEnv and lock
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handles. */
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open2(path, true);
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/* Try again. */
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open2(path, false);
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}
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else
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rethrow(e);
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}
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}
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@ -58,6 +58,8 @@ private:
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Db * getDb(TableId table);
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void open2(const string & path, bool removeOldEnv);
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public:
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Database();
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~Database();
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