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* Use Berkeley DB 4.4's process registry feature to recover from

Browse source 
crashed Nix instances, and toss out our own recovery code.
This commit is contained in:
Eelco Dolstra 2005-12-09 22:55:07 +00:00
parent eb268a7f95
commit a33b561a6b
2 changed files with 57 additions and 103 deletions
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157
src/libstore/db.cc
View file

@ -20,6 +20,16 @@ public:
};
class DestroyDbEnv
{
DbEnv * dbenv;
public:
DestroyDbEnv(DbEnv * _dbenv) : dbenv(_dbenv) { }
~DestroyDbEnv() { if (dbenv) { dbenv->close(0); delete dbenv; } }
void release() { dbenv = 0; };
};
static void rethrow(DbException & e)
{
throw Error(e.what());
@ -150,12 +160,17 @@ void setAccessorCount(int fd, int n)
}
void openEnv(DbEnv * env, const string & path, u_int32_t flags)
void openEnv(DbEnv * & env, const string & path, u_int32_t flags)
{
env->open(path.c_str(),
DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN |
DB_CREATE | flags,
0666);
try {
env->open(path.c_str(),
DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN |
DB_CREATE | flags,
0666);
} catch (DbException & e) {
printMsg(lvlError, format("environment open failed: %1%") % e.what());
throw;
}
}
@ -165,6 +180,18 @@ static int my_fsync(int fd)
}
static void errorPrinter(const DbEnv * env, const char * errpfx, const char * msg)
{
printMsg(lvlError, format("Berkeley DB error: %1%") % msg);
}
static void messagePrinter(const DbEnv * env, const char * msg)
{
printMsg(lvlError, format("Berkeley DB message: %1%") % msg);
}
void Database::open2(const string & path, bool removeOldEnv)
{
if (env) throw Error(format("environment already open"));
@ -173,8 +200,13 @@ void Database::open2(const string & path, bool removeOldEnv)
/* Create the database environment object. */
DbEnv * env = 0; /* !!! close on error */
env = new DbEnv(0);
DbEnv * env = new DbEnv(0);
DestroyDbEnv deleteEnv(env);
env->set_errcall(errorPrinter);
env->set_msgcall(messagePrinter);
//env->set_verbose(DB_VERB_REGISTER, 1);
env->set_verbose(DB_VERB_RECOVERY, 1);
/* Smaller log files. */
env->set_lg_bsize(32 * 1024); /* default */
@ -200,93 +232,19 @@ void Database::open2(const string & path, bool removeOldEnv)
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. */
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);
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 normally. */
openEnv(env, path, 0);
if (removeOldEnv) {
printMsg(lvlError, "removing old Berkeley DB database environment...");
env->remove(path.c_str(), DB_FORCE);
return;
}
openEnv(env, path, DB_REGISTER | DB_RECOVER);
deleteEnv.release();
this->env = env;
}
}
void Database::open(const string & path)
@ -310,6 +268,15 @@ void Database::open(const string & path)
/* Force a checkpoint, as per the BDB docs. */
env->txn_checkpoint(DB_FORCE, 0, 0);
}
#if 0
else if (e.get_errno() == DB_RUNRECOVERY) {
/* If recovery is needed, do it. */
printMsg(lvlError, "running recovery...");
open2(path, false, true);
}
#endif
else
rethrow(e);
}
@ -341,16 +308,6 @@ void Database::close()
} catch (DbException e) { rethrow(e); }
delete env;
/* Decrement the accessor count. */
lockFile(fdAccessors, ltWrite, true);
int n = getAccessorCount(fdAccessors) - 1;
setAccessorCount(fdAccessors, n);
debug(format("decremented accessor count to %1%") % n);
lockFile(fdAccessors, ltNone, true);
::close(fdAccessors);
::close(fdLock);
}

3
src/libstore/db.hh
View file

@ -48,9 +48,6 @@ class Database
private:
DbEnv * env;
int fdLock;
int fdAccessors;
TableId nextId;
map<TableId, Db *> tables;