Add mdb_env_info() to retrieve interesting env params

libraries/libmdb/mdb.c

@@ -6651,6 +6651,23 @@ mdb_env_stat(MDB_env *env, MDB_stat *arg)
 	return mdb_stat0(env, &env->me_metas[toggle]->mm_dbs[MAIN_DBI], arg);
 }
 
+int
+mdb_env_info(MDB_env *env, MDB_envinfo *arg)
+{
+	int toggle;
+
+	if (env == NULL || arg == NULL)
+		return EINVAL;
+
+	toggle = mdb_env_pick_meta(env);
+	arg->me_mapsize = env->me_mapsize;
+	arg->me_maxreaders = env->me_maxreaders;
+	arg->me_numreaders = env->me_numreaders;
+	arg->me_last_txnid = env->me_metas[toggle]->mm_txnid;
+	arg->me_last_pgno = env->me_metas[toggle]->mm_last_pg;
+	return MDB_SUCCESS;
+}
+
 /** Set the default comparison functions for a database.
  * Called immediately after a database is opened to set the defaults.
  * The user can then override them with #mdb_set_compare() or

libraries/libmdb/mdb.h

@@ -358,6 +358,15 @@ typedef struct MDB_stat {
 	size_t		ms_entries;			/**< Number of data items */
 } MDB_stat;
 
+/** @brief Information about the environment */
+typedef struct MDB_envinfo {
+	size_t	me_mapsize;				/**< Size of the data memory map */
+	size_t	me_last_txnid;			/**< ID of the last committed transaction */
+	size_t	me_last_pgno;			/**< ID of the last used page */
+	unsigned int me_maxreaders;		/**< maximum number of threads for the environment */
+	unsigned int me_numreaders;		/**< maximum number of threads used in the environment */
+} MDB_envinfo;
+
 	/** @brief Return the mdb library version information.
 	 *
 	 * @param[out] major if non-NULL, the library major version number is copied here
@@ -471,6 +480,14 @@ int  mdb_env_copy(MDB_env *env, const char *path);
 	 */
 int  mdb_env_stat(MDB_env *env, MDB_stat *stat);
 
+	/** @brief Return information about the MDB environment.
+	 *
+	 * @param[in] env An environment handle returned by #mdb_env_create()
+	 * @param[out] stat The address of an #MDB_envinfo structure
+	 * 	where the information will be copied
+	 */
+int  mdb_env_info(MDB_env *env, MDB_envinfo *stat);
+
 	/** @brief Flush the data buffers to disk.
 	 *
 	 * Data is always written to disk when #mdb_txn_commit() is called,

libraries/libmdb/mdb_stat.c

@@ -40,10 +40,11 @@ int main(int argc, char *argv[])
 	MDB_txn *txn;
 	MDB_dbi dbi;
 	MDB_stat mst;
+	MDB_envinfo mei;
 	char *prog = argv[0];
 	char *envname;
 	char *subname = NULL;
-	int alldbs = 0;
+	int alldbs = 0, envinfo = 0;
 
 	if (argc < 2) {
 		usage(prog);
@@ -51,13 +52,17 @@ int main(int argc, char *argv[])
 
 	/* -a: print stat of main DB and all subDBs
 	 * -s: print stat of only the named subDB
+	 * -e: print env info
 	 * (default) print stat of only the main DB
 	 */
-	while ((i = getopt(argc, argv, "as:")) != EOF) {
+	while ((i = getopt(argc, argv, "aes:")) != EOF) {
 		switch(i) {
 		case 'a':
 			alldbs++;
 			break;
+		case 'e':
+			envinfo++;
+			break;
 		case 's':
 			subname = optarg;
 			break;
@@ -87,6 +92,16 @@ int main(int argc, char *argv[])
 		printf("mdb_txn_begin failed, error %d %s\n", rc, mdb_strerror(rc));
 		goto env_close;
 	}
+
+	if (envinfo) {
+		rc = mdb_env_info(env, &mei);
+		printf("Map size: %zu \n", mei.me_mapsize);
+		printf("Last transaction ID: %zu\n", mei.me_last_txnid);
+		printf("Last page used: %zu\n", mei.me_last_pgno);
+		printf("Max readers: %u\n", mei.me_maxreaders);
+		printf("Number of readers used: %u\n", mei.me_numreaders);
+	}
+
 	rc = mdb_open(txn, subname, 0, &dbi);
 	if (rc) {
 		printf("mdb_open failed, error %d %s\n", rc, mdb_strerror(rc));