minor changes to doc and comments

redis.conf

@@ -291,77 +291,31 @@ appendfsync everysec
 # "no" that is the safest pick from the point of view of durability.
 no-appendfsync-on-rewrite no
 
-################################ VIRTUAL MEMORY ###############################
-
-# Virtual Memory allows Redis to work with datasets bigger than the actual
-# amount of RAM needed to hold the whole dataset in memory.
-# In order to do so very used keys are taken in memory while the other keys
-# are swapped into a swap file, similarly to what operating systems do
-# with memory pages.
-#
-# To enable VM just set 'vm-enabled' to yes, and set the following three
-# VM parameters accordingly to your needs.
-
-vm-enabled no
-# vm-enabled yes
-
-# This is the path of the Redis swap file. As you can guess, swap files
-# can't be shared by different Redis instances, so make sure to use a swap
-# file for every redis process you are running. Redis will complain if the
-# swap file is already in use.
-#
-# The best kind of storage for the Redis swap file (that's accessed at random) 
-# is a Solid State Disk (SSD).
-#
-# *** WARNING *** if you are using a shared hosting the default of putting
-# the swap file under /tmp is not secure. Create a dir with access granted
-# only to Redis user and configure Redis to create the swap file there.
-vm-swap-file /tmp/redis.swap
-
-# vm-max-memory configures the VM to use at max the specified amount of
-# RAM. Everything that deos not fit will be swapped on disk *if* possible, that
-# is, if there is still enough contiguous space in the swap file.
-#
-# With vm-max-memory 0 the system will swap everything it can. Not a good
-# default, just specify the max amount of RAM you can in bytes, but it's
-# better to leave some margin. For instance specify an amount of RAM
-# that's more or less between 60 and 80% of your free RAM.
-vm-max-memory 0
-
-# Redis swap files is split into pages. An object can be saved using multiple
-# contiguous pages, but pages can't be shared between different objects.
-# So if your page is too big, small objects swapped out on disk will waste
-# a lot of space. If you page is too small, there is less space in the swap
-# file (assuming you configured the same number of total swap file pages).
-#
-# If you use a lot of small objects, use a page size of 64 or 32 bytes.
-# If you use a lot of big objects, use a bigger page size.
-# If unsure, use the default :)
-vm-page-size 32
-
-# Number of total memory pages in the swap file.
-# Given that the page table (a bitmap of free/used pages) is taken in memory,
-# every 8 pages on disk will consume 1 byte of RAM.
-#
-# The total swap size is vm-page-size * vm-pages
-#
-# With the default of 32-bytes memory pages and 134217728 pages Redis will
-# use a 4 GB swap file, that will use 16 MB of RAM for the page table.
-#
-# It's better to use the smallest acceptable value for your application,
-# but the default is large in order to work in most conditions.
-vm-pages 134217728
-
-# Max number of VM I/O threads running at the same time.
-# This threads are used to read/write data from/to swap file, since they
-# also encode and decode objects from disk to memory or the reverse, a bigger
-# number of threads can help with big objects even if they can't help with
-# I/O itself as the physical device may not be able to couple with many
-# reads/writes operations at the same time.
-#
-# The special value of 0 turn off threaded I/O and enables the blocking
-# Virtual Memory implementation.
-vm-max-threads 4
+#################################### DISK STORE ###############################
+
+# When disk store is active Redis works as an on-disk database, where memory
+# is only used as a object cache.
+#
+# This mode is good for datasets that are bigger than memory, and in general
+# when you want to trade speed for:
+#
+#  - less memory used
+#  - immediate server restart
+#  - per key durability, without need for backgrond savig
+#
+# On the other hand, with disk store enabled MULTI/EXEC are no longer
+# transactional from the point of view of the persistence on disk, that is,
+# Redis transactions will still guarantee that commands are either processed
+# all or nothing, but there is no guarantee that all the keys are flushed
+# on disk in an atomic way.
+#
+# Of course with disk store enabled Redis is not as fast as it is when
+# working with just the memory back end.
+
+diskstore-enabled no
+diskstore-path redis.ds
+cache-max-memory 0
+cache-flush-delay 0
 
 ############################### ADVANCED CONFIG ###############################
 

src/db.c

@@ -19,7 +19,7 @@ robj *lookupKey(redisDb *db, robj *key) {
 
         if (server.ds_enabled && val->storage == REDIS_DS_SAVING) {
             /* FIXME: change this code to just wait for our object to
-             * get out of the IO Job. */
+             * get out of the IO Job. As it is now it is correct but slow. */
             waitEmptyIOJobsQueue();
             processAllPendingIOJobs();
             redisAssert(val->storage != REDIS_DS_SAVING);

src/dscache.c

@@ -109,6 +109,8 @@
  *   Also, make sure that key preloading is ONLY done for keys that are
  *   not marked as cacheKeyDoesNotExist(), otherwise, again, we can load
  *   data from disk that should instead be deleted.
+ *
+ * - dsSet() use rename(2) in order to avoid corruptions.
  */
 
 /* Virtual Memory is composed mainly of two subsystems: