Understanding Forests
A forest is a collection of XML, JSON, text, or binary documents. Forests are created on hosts and attached to databases to appear as a contiguous set of content for query purposes. A forest can only be attached to one database at a time. You cannot load data into a forest that is not attached to a database.
A forest contains in-memory and on-disk structures called stands. Each stand is composed of XML, JSON, binary, and/or text fragments, plus index information associated with the fragments. When fragmentation rules are in place, XML documents may span multiple stands. MarkLogic Server periodically merges multiple stands into a single stand to optimize performance. See Understanding and Controlling Database Merges for details on merges.
A forest also contains a separate on-disk Large Data Directory for storing large objects such as large binary documents. MarkLogic Server stores large objects separately to optimize memory usage, disk usage, and merge time. A small object is stored directly in a stand as a fragment. A large object is stored in a stand as a small reference fragment, with the full content stored in the Large Data Directory. The size threshold for storing objects in the Large Object Store and the location of the Large Object Store are configurable through the Admin Interface and Admin API. For details, see Working With Binary Documents in the Application Developer’s Guide.
By default, the operations allowed on a forest are: read, insert, update, and delete. You can control which operations are allowed on a forest by setting the following update types:
Update Type |
Description |
|---|---|
|
Read, insert, update, and delete operations are allowed on the forest. |
|
Read and delete operations are allowed on the forest, but insert and update operations are not allowed unless a forest ID is specified, in which case it results in the document being moved to another forest. If you do not specify a forest ID when updating a document in a delete-only forest, the update throws an exception. This update type is useful when you want to eliminate the overhead imposed by the merge operation, but still allow transactions to delete data from the forest. See Making a Forest Delete-Only for details. |
(Can only be set in Configure) |
Read operations are allowed on the forest, but insert, update, and delete operations are not allowed. A transaction attempting to make changes to fragments in the forest will throw an exception. This update type is useful when you want to put your forests on read-only media and allow them to be queried. See Making a Forest Read-Only for details. |
(Can only be set in Configure) |
This type puts the forest in read-only mode without throwing exceptions on insert, update, or delete transactions, allowing the transactions to retry. This update type is useful when you want to temporarily quiesce a forest or to disable changes to the forest data when doing a flash backup of the forest. See Making a Forest Read-Only for details. |
Note
To make the entire database read-only, set all of the forests in the database to read-only.