Method: LMDB::Environment#flags

Defined in:

ext/lmdb_ext/lmdb_ext.c

#flags ⇒ Array

Return the flags that are set in this environment. The environment flags are:

• :fixedmap Use a fixed address for the mmap region.

• :nosubdir By default, MDB creates its environment in a directory whose pathname is given in path, and creates its data and lock files under that directory. With this option, path is used as-is for the database main data file. The database lock file is the path with “-lock” appended.

• :nosync Don’t flush system buffers to disk when committing a transaction. This optimization means a system crash can corrupt the database or lose the last transactions if buffers are not yet flushed to disk. The risk is governed by how often the system flushes dirty buffers to disk and how often #sync is called. However, if the filesystem preserves write order and the :writemap flag is not used, transactions exhibit ACI (atomicity, consistency, isolation) properties and only lose D (durability). That is, database integrity is maintained, but a system crash may undo the final transactions. Note that :nosync :writemap+ leaves the system with no hint for when to write transactions to disk, unless #sync is called. :mapasync :writemap+ may be preferable.

• :rdonly Open the environment in read-only mode. No write operations will be allowed. MDB will still modify the lock file - except on read-only filesystems, where MDB does not use locks.

• :nometasync Flush system buffers to disk only once per transaction, omit the metadata flush. Defer that until the system flushes files to disk, or next non-MDB_RDONLY commit or #sync. This optimization maintains database integrity, but a system crash may undo the last committed transaction. That is, it preserves the ACI (atomicity, consistency, isolation) but not D (durability) database property.

• :writemap Use a writeable memory map unless :rdonly is set. This is faster and uses fewer mallocs, but loses protection from application bugs like wild pointer writes and other bad updates into the database. Incompatible with nested transactions.

• :mapasync When using :writemap, use asynchronous flushes to disk. As with :nosync, a system crash can then corrupt the database or lose the last transactions. Calling #sync ensures on-disk database integrity until next commit.

• :notls Don’t use thread-local storage.

Examples:

env = LMDB.new "abc", :writemap => true, :nometasync => true
env.flags           #=> [:writemap, :nometasync]

Returns:

• Array of flag symbols

# File 'ext/lmdb_ext/lmdb_ext.c', line 684

static VALUE environment_flags(VALUE self) {
        unsigned int flags;
        ENVIRONMENT(self, environment);
        check(mdb_env_get_flags(environment->env, &flags));

        VALUE ret = rb_ary_new();
#define FLAG(const, name) if (flags & MDB_##const) rb_ary_push(ret, ID2SYM(rb_intern(#name)));
#include "env_flags.h"
#undef FLAG

        return ret;
}