When you use JindoFS in cache mode, files are stored as objects in Object Storage Service (OSS), and the frequently used files are cached in an EMR cluster to improve the data access efficiency. In cache mode, JindoFS can access files in OSS without the need to convert the file formats, and JindoFS is fully compatible with OSS clients. This topic describes how to use JindoFS in cache mode.

Background information

In cache mode, JindoFS supports the object semantics of OSS and is fully compatible with various OSS clients. This ensures that you can access files in OSS without the need to migrate data or convert data formats. In cache mode, JindoFS caches frequently used files in an EMR cluster. This improves the read and write performance and relieves pressure on bandwidth.

In cache mode, you can use one of the following methods to access files in Object Storage Service (OSS) based on your business requirements:

Method 1: (Recommended) Configure OSS Scheme

OSS Scheme refers to the original method of accessing files in OSS. You can use the oss://<bucket_name>/<path_of_your_file> command to access files in OSS. After you create an EMR cluster, you can use this method to access files in OSS without additional configurations. You can also run existing jobs to read or write data from or to OSS without the need to modify the configurations.

  1. Enable local cache
  2. Control disk space usage
  3. Optional:Access an OSS bucket
  4. Optional:Configure advanced parameters

Method 2: Configure JFS Scheme

  1. Configure JFS Scheme
  2. Enable local cache
  3. Control disk space usage
  4. Optional:Access an OSS bucket
  5. Optional:Configure advanced parameters

Configure JFS Scheme

  1. Go to the SmartData service.
    1. Log on to the Alibaba Cloud EMR console.
    2. In the top navigation bar, select the region where your cluster resides. Select the resource group as required. By default, all resources of the account appear.
    3. Click the Cluster Management tab.
    4. On the Cluster Management page that appears, find the target cluster and click Details in the Actions column.
    5. In the left-side navigation pane, click Cluster Service and then SmartData.
  2. Go to the namespace tab for the SmartData service.
    1. Click the Configure tab.
    2. Click the namespace tab in the Service Configuration section.
      namespace
  3. Configure the required parameters.
    JindoFS allows you to configure multiple namespaces. A namespace named test is used in this topic.
    1. Set jfs.namespaces to test.
      If you configure multiple namespaces, separate them with commas (,).
    2. Click Custom Configuration. In the Add Configuration Item dialog box, configure the parameters described in the following table and click OK.
      Parameter Description Example
      jfs.namespaces.test.oss.uri The storage backend of the test namespace. oss://<oss_bucket>/<oss_dir>/
      Note Set this parameter to a directory for a specific OSS bucket or the root directory.
      jfs.namespaces.test.mode The storage mode of the test namespace. Set this parameter to cache. cache
  4. Click OK.
  5. Save the configurations.
    1. In the upper-right corner of the Service Configuration section, click Save.
    2. In the Confirm Changes dialog box, specify Description and turn on Auto-update Configuration.
    3. Click OK.
  6. Select Restart Jindo Namespace Service from the Actions drop-down list in the upper-right corner.
    After Namespace Service is restarted, you can use jfs://test/<path_of_file> to access files in JindoFS.

Enable local cache

After you enable local cache, hot data blocks are cached on local disks. By default, this feature is disabled, and EMR directly reads data from OSS.

  1. On the Configure tab of the SmartData service page, click the client tab.
  2. Set jfs.cache.data-cache.enable to true to enable local cache.
    You do not need to restart the SmartData service.
  3. Save the configurations.
    1. In the upper-right corner of the Service Configuration section, click Save.
    2. In the Confirm Changes dialog box, specify Description and turn on Auto-update Configuration.
    3. Click OK.

After you enable local cache, Jindo automatically manages cached data. It clears the cache based on the specified upper and lower limits of disk usage. For more information about how to configure the limits, see Control disk space usage.

Control disk space usage

JindoFS uses OSS as the data storage backend, which allows you to store large volumes of data. However, the capacity of local disks is limited. JindoFS automatically deletes cold data in local disks. The storage.watermark.high.ratio and storage.watermark.low.ratio parameters are used to adjust the space usage of local disks. You can set the parameters to decimal numbers between 0 and 1.

  1. Modify disk usage configurations.
    In the Service Configuration section for the SmartData service, click the storage tab and configure the parameters described in the following table. storage
    Parameter Description
    storage.watermark.high.ratio The upper limit of disk usage. When the disk usage of JindoFS data exceeds this limit, JindoFS automatically deletes data in the disk. Default value: 0.4.
    storage.watermark.low.ratio The lower limit of disk usage. After automatic data deletion is triggered, JindoFS starts to delete data until the disk usage of JindoFS data is reduced to this limit. Default value: 0.2.
    Note You can configure the upper limit and lower limit to adjust the disk space assigned to JindoFS. Make sure that the upper limit is greater than the lower limit.
  2. Save the configurations.
    1. In the upper-right corner of the Service Configuration section, click Save.
    2. In the Confirm Changes dialog box, specify Description and turn on Auto-update Configuration.
    3. Click OK.
  3. Restart Jindo Storage Service to apply the configurations.
    1. Select Restart Jindo Storage Service from the Actions drop-down list in the upper-right corner.
    2. In the Cluster Activities dialog box, specify the related parameters.
    3. Click OK.
    4. In the Confirm message, click OK.

Access an OSS bucket

If you access an OSS bucket that is within the same Alibaba Cloud account and in the same region as your EMR cluster, you do not need to specify an AccessKey pair. In other cases, you must specify an AccessKey pair and an OSS endpoint. Configure the parameters based on the method that you use to access files in OSS:
  • OSS Scheme
    1. On the Configure tab of the SmartData service page, click the smartdata-site tab.
    2. On the smartdata-site tab, click Custom Configuration.
    3. In the Add Configuration Item dialog box, add the following parameters.
      Parameter Description
      fs.jfs.cache.oss.accessKeyId The AccessKey ID used to access the OSS bucket that serves as the storage backend.
      fs.jfs.cache.oss.accessKeySecret The AccessKey secret used to access the OSS bucket that serves as the storage backend.
      fs.jfs.cache.oss.endpoint The endpoint of the OSS bucket that serves as the storage backend.
      Note You are also allowed to use the configuration items in EMR versions earlier than V3.30.0.
    4. Click OK.
  • JFS Scheme
    1. On the Configure tab of the SmartData service page, click the namespace tab.
    2. On the namespace tab, set jfs.namespaces to test.

      A namespace named test is used in this example.

    3. Click Custom Configuration in the upper-right corner.
    4. In the Add Configuration Item dialog box, add the following parameters.
      Parameter Description
      jfs.namespaces.test.oss.uri The storage backend of the test namespace. Example: oss://<oss_bucket.endpoint>/<oss_dir>.

      The endpoint of the OSS bucket is specified in this parameter.

      jfs.namespaces.test.oss.access.key The AccessKey ID used to access the OSS bucket that serves as the storage backend.
      jfs.namespaces.test.oss.access.secret The AccessKey secret used to access the OSS bucket that serves as the storage backend.
    5. Click OK.

Configure advanced parameters

You can configure some advanced parameters to optimize the cache performance. After you configure the parameters, you do not need to restart the SmartData service.

  • In the Service Configuration section, click the client tab and configure the following parameters.
    Parameter Description
    client.oss.upload.threads The number of OSS upload threads for each data write stream. Default value: 4.
    client.oss.upload.max.parallelism The maximum number of concurrent OSS upload threads of a process. You can use this parameter to prevent upload threads from occupying an excessive amount of bandwidth and memory. Default value: 16.
  • In the Service Configuration section, click the smartdata-site tab and configure the following parameters.
    Parameter Description
    fs.jfs.cache.write.buffer.size The buffer size of data write streams. Unit: bytes. You must set this parameter to a power of 2. The maximum value is 8388608 (8 MB). If an excessive amount of memory is occupied by write streams, we recommend that you set this parameter to a small value. Default value: 1048576.
    fs.oss.committer.magic.enabled Specifies whether to enable Jindo Job Committer. Job Committer does not require rename operations and therefore improves job commit performance. Default value: true.
    Note In cache mode, the performance of renaming files in OSS is less than standard. We recommend that you use Jindo Job Committer.