Transient Store

A Transient Store allows you to store temporary blobs and associated parameters (file name, MIME type, etc.) in a Nuxeo instance but outside of the document repository, thus the "transient" aspect.

It is typically used by:

• The Batch Upload API to temporarily store a batch of uploaded blobs until they are attached to a document.
• The ConversionService to store the BlobHolder resulting from an Asynchronous Conversion Work.
• The BatchHandler contributions that interact with the Transient Store.

The TransientStore API is based on the following methods:

void putBlobs(String key, List blobs);
void putParameter(String key, String parameter, Serializable value);
void putParameters(String key, Map parameters);

List getBlobs(String key);
Serializable getParameter(String key, String parameter);
Map getParameters(String key);

Configuration

You can configure any number of transient stores with the following extension point:

<extension target="org.nuxeo.ecm.core.transientstore.TransientStorageComponent"
  point="store">
  <store name="foobar" class="...">
    <targetMaxSizeMB>-1</targetMaxSizeMB>
    <absoluteMaxSizeMB>-1</absoluteMaxSizeMB>
    <firstLevelTTL>240</firstLevelTTL>
    <secondLevelTTL>10</secondLevelTTL>
    <!--
       Optional, may be used with the KeyValueBlobTransientStore
       if you don't want the default naming.
    <property name="keyValueStore">transient_foobar</property>
    <property name="blobProvider">transient_foobar</property>
    -->
</store>
</extension>

The store element supports two attributes:

• name: Used to identify the transient store.
• class: Optionally references an implementation of the TransientStore interface (the default is to use the same class as the default transient store, which is KeyValueBlobTransientStore by default).

The nested configuration elements are:

• targetMaxSizeMB: The target size that ideally should never be exceeded.
• absoluteMaxSizeMB: The size that must never be exceeded.
• firstLevelTTL: TTL in minutes of the first level cache.
• secondLevelTTL: TTL in minutes of the second level cache.

Two additional properties can be defined if the KeyValueBlobTransientStore is used:

• keyValueStore: The key/value store name.
• blobProvider: The blob provider name.

Both of these names default to transient_ followed by the transient store name.

Have a look at the default transient store configuration, defined in a template:

<?xml version="1.0"?>
<component name="org.nuxeo.ecm.core.transient.store.config">
  <extension target="org.nuxeo.ecm.core.transientstore.TransientStorageComponent"
    point="store">
    <store name="default" class="org.nuxeo.ecm.core.transientstore.keyvalueblob.KeyValueBlobTransientStore">
      <targetMaxSizeMB>-1</targetMaxSizeMB>
      <absoluteMaxSizeMB>-1</absoluteMaxSizeMB>
      <firstLevelTTL>240</firstLevelTTL>
      <secondLevelTTL>10</secondLevelTTL>
    </store>
  </extension>
</component>

To retrieve a given transient store, just call TransientStoreService#getStore(String name). If the specified transient store hasn't been registered, the default one is used instead.

Implementation

Other implementations than KeyValueBlobTransientStore can be used, but this is the recommended one. If you use the redis template and want to use the old RedisTransientStore, you must set nuxeo.transientstore.provider=redis.

Blob Storage

The KeyValueBlobTransientStore stores its blobs in a BlobProvider. You can either specify the name of the blob provider to use with <property name="blobProvider">myblobprovider</property>, or let it default to transient_ followed by the transient store name.

If a blob provider is referenced but there is no actual XML configuration for it, a configuration based on the default blob provider will be used, however with a "namespace" to avoid collisions. For the file-based blob provider, this will be in a directory named binaries_ followed by the blob provider name. For S3 or Azure, this will be in a "subfolder" of the bucket/container named from the blob provider name.

It's important to mark the blob provider as transient in its configuration using <property name="transient">true</property>. This is done implicitly if the blob provider names starts with transient.

Parameter Storage

The KeyValueBlobTransientStore stores its parameters in a KeyValueStore. You can either specify the name of the key/value store to use with <property name="keyValueStore">mykeyvaluestore</property>, or let it default to transient_ followed by the transient store name.

If a key/value store is referenced but there is no actual XML configuration for it, a configuration based on the default key/value store will be used, however with a "namespace" to avoid collisions.

The default key/value store in Nuxeo templates is SQLKeyValueStore if a SQL database is used, or MongoDBKeyValueStore if MongoDB is used.

Time To Live and Garbage Collector

Entries have a Time To Live (TTL) defined in the transient store configuration.

Initially the TTL of an entry is set to firstLevelTTL. It can later be set to secondLevelTTL by calling TransientStore#release(String key).

The garbage collection:

• Is scheduled every 15 minutes to wipe the files associated to entries that don't exist anymore.
• Can be triggered manually on a given store with TransientStore#doGC or all stores with TransientStoreService#doGC.

Example Services Using a Transient Store

BatchManager

It relies on the BatchManagerCache transient store which in fact is not registered so it falls back on the default transient store, this is to allow overriding the configuration if needed.

See the "Batch Upload Example" section of NXP-18050 for details.

TransientStoreWork

A Work allowing to store a result in a transient store.

It relies on the transientStoreWorkCache transient store, also not registered with a fallback on the default transient store.

For example, the Asynchronous Conversions rely on such instances of TransientStoreWork via the ConversionWork class.