MARKLOGIC SERVER

if the global commit happened or not. There are special handling abilities should the
TM fail longer than temporarily at the critical moment, such that the commit state
could be ambiguous.
STORAGE TYPES WITHIN A FOREST
In the next short section, we'll see how MarkLogic uses different storage types to
maximize performance while minimizing storage costs within the same forest.
The "Tiered Storage" section discusses moving whole forests between different
storage tiers.
FAST DATA DIRECTORY ON SSDS
Solid-state drives (SSDs) perform dramatically better than spinning hard disks, at a
price that's substantially higher. The price is high enough that only deployments against
the smallest data sets would want to host all of their forest data on SSDs. To get some
of the benefits of SSD performance without the cost, MarkLogic has a configurable
"fast data directory" for each forest, which you set up to point to a directory built on
a fast filesystem (such as one using SSDs). It's completely optional. If it's not present,
then nothing special happens and all the data is placed in the regular "data directory."
But if it is present, then each time a forest does a checkpoint or a merge, MarkLogic
will attempt to write the new stand to the fast data directory. When it can't because
there's no room, it will use the regular data directory. Of course, merging onto the
"data directory" will then free up room on the fast data directory for future stands. The
journals for the forest will also be placed on the fast data directory. As a result, all of the
checkpoints and the smaller and more frequent merges will happen on SSD, improving
utilization of disk I/O bandwidth. Note that frequently updated documents tend to
reside in the smaller stands and thus are more likely to reside on the SSD.
Testing shows that making 5% to 10% of a system's storage capacity solid state provides
good bang for the buck. Note that if you put solid-state storage in a system, it should be
SLC flash (for its higher performance, reliability, and life span) and either be PCI-based
or have a dedicated controller.
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