Commit ab9b08f8 authored by Howard Chu's avatar Howard Chu
Browse files

ITS#7725 add MDB_NORDAHEAD flag for env_open

parent 5a9ddfd2
......@@ -275,6 +275,8 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
#define MDB_NOTLS 0x200000
/** don't do any locking, caller must manage their own locks */
#define MDB_NOLOCK 0x400000
/** don't do readahead (no effect on Windows) */
#define MDB_NORDAHEAD 0x800000
/** @} */
/** @defgroup mdb_dbi_open Database Flags
......@@ -538,6 +540,12 @@ int mdb_env_create(MDB_env **env);
* that no readers are using old transactions while a writer is
* active. The simplest approach is to use an exclusive lock so that
* no readers may be active at all when a writer begins.
* Turn off readahead. Most operating systems perform readahead on
* read requests by default. This option turns it off if the OS
* supports it. Turning it off may help random read performance
* when the DB is larger than RAM and system RAM is full.
* The option is not implemented on Windows.
* </ul>
* @param[in] mode The UNIX permissions to set on created files. This parameter
* is ignored on Windows.
......@@ -3283,6 +3283,8 @@ mdb_env_map(MDB_env *env, void *addr, int newsize)
env->me_map = NULL;
return ErrCode();
if (flags & MDB_NORDAHEAD) {
/* Turn off readahead. It's harmful when the DB is larger than RAM. */
madvise(env->me_map, env->me_mapsize, MADV_RANDOM);
......@@ -3291,6 +3293,7 @@ mdb_env_map(MDB_env *env, void *addr, int newsize)
posix_madvise(env->me_map, env->me_mapsize, POSIX_MADV_RANDOM);
#endif /* POSIX_MADV_RANDOM */
#endif /* MADV_RANDOM */
#endif /* _WIN32 */
/* Can happen because the address argument to mmap() is just a
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