* Automatically upgrade the Berkeley DB environment if necessary.

This commit is contained in:
Eelco Dolstra 2005-05-09 15:25:47 +00:00
parent 88dea78cdf
commit 8f57634c14
2 changed files with 134 additions and 107 deletions

View file

@ -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). */
/* 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 */
/* !!! 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);
}
/* 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);
else
/* Open the environment normally. */
openEnv(env, path, 0);
setAccessorCount(fdAccessors, 1);
/* 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"));
/* 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 after running recovery. */
openEnv(env, path, DB_RECOVER);
}
else
/* Open the environment normally. */
openEnv(env, path, 0);
}
this->env = env;
setAccessorCount(fdAccessors, 1);
/* 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"));
/* Acquire a read lock. */
debug(format("acquiring read lock on `%1%'") % lockPath);
lockFile(fdLock, ltRead, true); /* wait indefinitely */
} catch (DbException e) { rethrow(e); }
/* 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;
}
void Database::open(const string & path)
{
try {
open2(path, false);
} 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);
}
}

View file

@ -58,6 +58,8 @@ private:
Db * getDb(TableId table);
void open2(const string & path, bool removeOldEnv);
public:
Database();
~Database();