Added documentation for RocksDB and hash cache options to manual.

Documentation/Books/Manual/Administration/Configuration/Cache.md

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+Hash cache options
+==================
+
+Since ArangoDB 3.2, the several core components of the server use a cache system
+which pools memory across many different cache tables. In order to provide
+intelligent internal memory management, the system periodically reclaims memory
+from caches which are used less often and reallocates it to caches which get
+more activity.
+
+### Cache size
+
+Global size limit for all hash caches: `--cache.size`
+
+The global caching system, all caches, and all the data contained therein will
+fit inside this limit. The size is specified in bytes. If there is less than 4GB
+of RAM on the system, the default value is 256MB. If there is more,
+the default is `(system RAM size - 2GB) * 0.3`.
+
+### Rebalancing interval
+
+Time between cache rebalancing attempts: `--cache.rebalancing-interval`
+
+The value is specified in microseconds with a default of 2 seconds and a
+minimum of 500 milliseconds.

Documentation/Books/Manual/Administration/Configuration/RocksDB.md

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+RocksDB engine options
+======================
+
+RocksDB is a highly configurable key-value store used to power our RocksDB
+storage engine. Most of the options on this page are pass-through options to the
+underlying RocksDB instance, and we change very few of their default settings.
+
+## Pass-through options
+
+### Write buffers
+
+`--rocksdb.write-buffer-size`
+
+The amount of data to build up in each in-memory buffer (backed by a log file)
+before closing the buffer and queueing it to be flushed into standard storage.
+Default: 64MB. Larger values may improve performance, especially for bulk
+loads.
+
+`--rocksdb.max-write-buffer-number`
+
+The maximum number of write buffers that built up in memory. If this number is
+reached before the buffers can be flushed, writes will be slowed or stalled.
+Default: 2.
+
+`--rocksdb.min-write-buffer-number-to-merge`
+
+Minimum number of write buffers that will be merged together when flushing to
+normal storage. Default: 1.
+
+`--rocksdb.delayed_write_rate` (Hidden)
+
+### LSM tree structure
+
+Limited write rate to DB (in bytes per second) if we are writing to the last
+in-memory buffer allowed and we allow more than 3 buffers. Default: 16MB/s.
+
+`--rocksdb.num-levels`
+
+The number of levels for the database in the LSM tree. Default: 7.
+
+`--rocksdb.max-bytes-for-level-base` (Hidden)
+
+The maximum total data size in bytes in level-1 of the LSM tree. Default: 256MB.
+
+`--rocksdb.max-bytes-for-level-multiplier`
+
+The maximum total data size in bytes for level L of the LSM tree can be
+calculated as `max-bytes-for-level-base * (max-bytes-for-level-multiplier ^
+(L-1))`. Default: 10.
+
+### File I/O
+
+`--rocksdb.compaction-read-ahead-size` (Hidden)
+
+If non-zero, we perform bigger reads when doing compaction. If you're  running
+RocksDB on spinning disks, you should set this to at least 2MB. That way
+RocksDB's compaction is doing sequential instead of random reads. Default: 0.
+
+`--rocksdb.use-direct-reads` (Hidden)
+
+Only meaningful on Linux. If set, use `O_DIRECT` for reading files. Default:
+false.
+
+`--rocksdb.use-direct-writes` (Hidden)
+
+Only meaningful on Linux. If set,use `O_DIRECT` for writing files. Default:
+true.
+
+`--rocksdb.use-fsync` (Hidden)
+
+If set, issue an `fsync` call when writing to disk (set to false to issue
+`fdatasync` only. Default: false.
+
+### Background tasks
+
+`--rocksdb.base-background-compactions` (Hidden)
+
+Suggested number of concurrent background compaction jobs, submitted to the low
+priority thread pool. Default: 1.
+
+`--rocksdb.max-background-compactions`
+
+Maximum number of concurrent background compaction jobs, submitted to the low
+priority thread pool. Default: 1.
+
+`--rocksdb.max-background-flushes`
+
+Maximum number of concurrent flush operations, submitted to the high priority
+thread pool. Default: 1.
+
+`--rocksdb.num-threads-priority-high`
+
+Number of threads for high priority operations (e.g. flush). We recommend
+setting this equal to `max-background-flushes`. Default: 1.
+
+`--rocksdb.num-threads-priority-low`
+
+Number of threads for low priority operations (e.g. compaction). We recommend
+setting this equal to `max-background-compactions`. Default: 1.
+
+### Caching
+
+`--rocksdb.block-cache-size`
+
+This is the size of the block cache in bytes. Increasing this may improve
+performance. Default: 8MB.
+
+`--rocksdb.block-cache-shard-bits`
+
+The number of bits used to shard the block cache to allow concurrent operations.
+To keep individual shards at a reasonable size (i.e. at least 512KB), keep this
+value to at most `block-cache-shard-bits / 512KB`. Default: 4.
+
+### Logging
+
+`--rocksdb.max-log-file-size` (Hidden)
+
+Specify the maximal size of the info log file. When the file size is reached, a
+new file will be created. If set to 0, everything will be written to one file.
+Default: 0.
+
+`--rocksdb.keep-log-file-num` (Hidden)
+
+The maximum number of info log files to be kept. Default: 1000.
+
+`--rocksdb.recycle-log-file-num` (Hidden)
+
+Number of log files to keep around for recycling. Default: 0.
+
+`--rocksdb.log-file-time-to-roll` (Hidden)
+
+Time for the info log file to roll (in seconds). If specified with non-zero
+value, log file will be rolled if it has been active longer than
+`log_file_time_to_roll`. Set to 0 to disable. Default: 0.
+
+### Miscellaneous
+
+`--rocksdb.verify-checksums-in-compaction` (Hidden)
+
+If true, compaction will verify the data checksum on every read that happens as
+part of compaction. Default: true;
+
+`--rocksdb.optimize-filters-for-hits` (Hidden)
+
+This flag specifies that the implementation should optimize the filters mainly
+for cases where keys are found rather than also optimize for the case where
+keys are not. This would be used in cases where the application knows that
+there are very few misses or the performance in the case of misses is not as
+important. Default: false.
+
+`--rocksdb.wal-recovery-skip-corrupted` (Hidden)
+
+If true, skip corrupted records in WAL recovery. Default: false.
+
+## Non-Pass-Through Options
+
+`--rocksdb.max-transaction-size`
+
+Transaction size limit (in bytes). Transactions store all keys and values in
+RAM, so large transactions run the risk of causing out-of-memory sitations.
+This setting allows you to ensure that does not happen by limiting the size of
+any individual transaction. Default: `UINT64_MAX` (`2^64 - 1`).
+
+`--rocksdb.intermediate-transaction` (Hidden)
+
+Enable intermediate commits. Default: false.
+
+`--rocksdb.intermediate-transaction-count` (Hidden)
+
+If intermediate commits are enabled, one will be tried when a transaction has
+accumulated operations totalling this size (in bytes). Default: 32MB.
+
+`--rocksdb.wal-file-timeout` (Hidden)
+
+Timeout after which unused WAL files are deleted (in seconds). Default: 10.0s.

Documentation/Books/Manual/SUMMARY.md

@@ -158,6 +158,8 @@
     * [General Options](Administration/Configuration/GeneralArangod.md)
     * [Write-Ahead Log Options](Administration/Configuration/Wal.md)
     * [Cluster Options](Administration/Configuration/Cluster.md)
+    * [RocksDB Engine Options](Administration/Configuration/RocksDB.md)
+    * [Hash Cache Options](Administration/Configuration/Cache.md)
     * [Asynchronous Tasks](Administration/Configuration/Asynchronous.md)
   * [Durability](Administration/Durability.md)
   * [Replication](Administration/Replication/README.md)