Implement Multi Part AOF mechanism to avoid AOFRW overheads.

redis.conf

@@ -1330,10 +1330,34 @@ disable-thp yes
 
 appendonly no
 
-# The name of the append only file (default: "appendonly.aof")
+# The base name of the append only file.
+# 
+# Redis can persist the data to a set of append-only files, they are divided
+# into two types, one is the the base type, it represents an initial (RDB
+# or AOF format) snapshot of the data present when the AOF is rewritten. The 
+# others are incremental type, they contain the incremental commands since the last 
+# base AOF file was created.
+# 
+# In order to manage these AOF files, Redis uses a manifest file to track them.
+# 
+# These files mentioned above have a certain naming rule. The appendfilename
+# config will be used as the base part of the file name, which will be added
+# suffixes to denote role and sequence number.
+# 
+# For example: 
+#
+# The base could be: appendonly.aof.1.base.rdb
+# The incremental ones: appendonly.aof.1.incr.aof, appendonly.aof.2.incr.aof
+# The manifest file: appendonly.aof.manifest
 
 appendfilename "appendonly.aof"
 
+# The directory name of the append only files.
+#
+# All AOF files and manifest file will be placed in this directory.
+
+appenddirname "appendonlydir"
+
 # The fsync() call tells the Operating System to actually write data on disk
 # instead of waiting for more data in the output buffer. Some OS will really flush
 # data on disk, some other OS will just try to do it ASAP.
@@ -1426,15 +1450,11 @@ auto-aof-rewrite-min-size 64mb
 # will be found.
 aof-load-truncated yes
 
-# When rewriting the AOF file, Redis is able to use an RDB preamble in the
-# AOF file for faster rewrites and recoveries. When this option is turned
-# on the rewritten AOF file is composed of two different stanzas:
-#
-#   [RDB file][AOF tail]
-#
-# When loading, Redis recognizes that the AOF file starts with the "REDIS"
-# string and loads the prefixed RDB file, then continues loading the AOF
-# tail.
+# The base AOF encodeing type.
+# 
+# The base file can be in AOF (commands) format or RDB (serialized) format. 
+# When this option is turned on, the base file uses RDB format, otherwise 
+# it uses AOF format.
 aof-use-rdb-preamble yes
 
 # Redis supports recording timestamp annotations in the AOF to support restoring