Table of Contents

Using the Remote Crawler

Without the Ultra Search remote crawler, you must run the Ultra Search Crawler on the same host as the Oracle9i Server. For large data sets, you can improve performance by running the Ultra Search Crawler on one or more separate hosts from the Oracle 9i Server. Since the Ultra Search Crawler is a pure Java application, it communicates with the Oracle9i Server via JDBC.

Ultra Search remote crawlers instances are always launched by the Oracle9i Server. The Oracle9i Server uses Java Remote Method Invocation (RMI) to communicate with the remote crawler hosts. Therefore, each remote host must have an RMI Registry and an RMI Daemon up and running.

The reason for launching remote crawlers from the Oracle9i Server is to leverage the high-availability of the Oracle9i Server. The Ultra Search scheduling mechanism runs within the Oracle9i Server and therefore automatically uses the database's high availability features.

Scalability and Load Balancing

Each Ultra Search schedule can be associated with exactly one crawler. The crawler can run locally on the Oracle9i Server host or on a remote host. There is no limit to the number of schedules that can be run. Similarly, there is no limit to the number of Remote Crawler hosts that can be run.

However, each remote crawler host requires that the Ultra Search Middle-Tier Components be installed on its host.

By using several remote crawler hosts and carefully allocating schedules to specific hosts, you can achieve scalability and load balancing of the entire crawling process.

How is this "launching" achieved?

It is done using Java Remote Method Invocation (RMI) technology.

Step 1: When a crawling schedule is activated, the Ultra Search scheduler launches a Java program as a separate process on the database host. We shall refer to this Java program as the ActivationClient.

Step 2: This program attempts to connect to the remote crawler host via the standard RMI Registry and RMI Daemon on ports 1098 and 1099. If successful, the ActivationClient receives a remote reference to a Java object running on the remote host. This remote Java object is known as the ActivatableCrawlerLauncher.

Step 3: The ActivationClient then instructs the ActivatableCrawlerLauncher to launch the Ultra Search Crawler on the remote host. The ActivatableCrawlerLauncher launches the Ultra Search Crawler as a separate Java process on the remote host.

Installation & Configuration sequence

  1. Make sure that you have installed the Ultra Search Server Component on the Oracle9i Server.

    See Installing Oracle Ultra Search

  2. Make sure that you have installed the Ultra Search Middle-Tier Components on one or more web server hosts.

    See Installing Oracle Ultra Search
  3. Install the Ultra Search Middle-Tier Components on all Remote Crawler hosts.

    See Installing Oracle Ultra Search
  4. Export the following common resources on the database host:

    1. The temporary directory
    2. The log directory
    3. mail archive directory (only if you are using the Ultra Search mailing list feature)

    These resources are merely directories that must be accessible by all remote crawler instances over the network. You can use whatever mechanism you wish to share these resources with a remote crawler host.

    The remote crawler code is pure Java. Therefore it is platform independent. For example, your Ultra Search installation may consist of 4 hosts. One database server (host X) on which the Ultra Search server component is installed. This host is running Solaris. One remote crawler host (host Y1) running on Windows NT. One remote crawler host (host Y2) running on Solaris. One Remote Crawler host (host Y3) running on Linux.

    In this scenario, you export the shared directories on host X using the unix "export" command. You then use the unix "mount" command on hosts Y2 and Y3 to mount the exported directories. For host Y1, you have to purchase a third-party NFS client for Windows NT and use that to mount the shared directories. (Note that if host X was a linux server, you can create Samba shares and thereby mount those shares on Windows NT without needing to purchase any third party software).

  5. Configure the remote crawler via the Administration Tool.

    You will now have to edit that profile by manually entering all mount points for the shared crawler resources that you defined in step 4. To edit the remote crawler profile, navigate to the "Crawler : remote crawler Profiles" page and click on the edit icon of the remote crawler profile you wish to edit:

    Specify values for the following parameters:

    • Mount point for temporary directory path as seen by the remote crawler
    • Mount point for log directory path as seen by the Remote Crawler
    • Mount point for mail archive path as seen by the Remote Crawler (only if you are using the Ultra Search mailing list feature)

    Additionally, you must specify the following crawler parameters before you can begin crawling:

    • Number of crawler threads that the remote crawler uses for gathering documents.
    • Number of processors on the remote crawler host.
  6. Complete the crawler configuration via the Administration Tool.

    Consult the Ultra Search Administration Tool documentation for details. The minimum set of parameters that will likely need to be configured are:

    • Seed urls
    • Web Proxy
    • A schedule

    Note that each schedule must be assigned to a remote crawler or the local crawler (the local crawler is the crawler that runs on the local Oracle9i database host itself). To assign the a schedule to a remote crawler host or the local database host, click on the hostname of a schedule in the "Synchronization Schedules" page.

    Note that you can also "turn off" the remote crawler feature for each schedule, thereby forcing the the schedule to launch a crawler on the local database host instead of the specified remote crawler host. To "turn off" the remote crawler feature, click on the hostname of a schedule in the "Synchronization Schedules" page. If a remote crawler host is selected, you will be able to enable or disable the remote crawler.

  7. Start up the RMI registry and RMI daemon on each Remote Crawler host.

    You can use the helper scripts in $WEB_ORACLE_HOME/tools/remotecrawler/scripts/ to do so.

    If the remote crawler is running on a unix platform, you can source the $WEB_ORACLE_HOME/tools/remotecrawler/scripts/unix/ Bourne shell script.

    If the remote crawler is running on a windows NT host, you can run the
    %WEB_ORACLE_HOME%\tools\remotecrawler\scripts\winnt\runall.bat file.

    The and runall.bat scripts perform the following tasks in sequence:

    • define_env is invoked to define necessary environment variables
    • runregistry is invoked to start up the RMI Registry
    • runrmid is invoked to start up the RMI Daemon
    • register_stub is invoked to register the necessary Java classes with the RMI subsystem

    You can invoke runregistry, runrmid and register_stub individually. However, you must first invoke define_env to define the necessary environment variables.

  8. Launch the remote crawler from the Administration Tool and verify that it is running.

    The state of the schedule is listed in the Schedules page. Please be patient as the remote crawler launching process will take up to 90 seconds to change state from LAUNCHING to FAILED if failure occurs.

    To view the schedule status, click on the crawler status in the schedules list. To view more details especially in the event of failure, click on the schedule status itself. This will bring up a detailed schedule status page.

    The remote crawler will fail to launch if any one of the following requirements are not met:

    1. The RMI registry is not running and listening on port 1099 of each remote host.
    2. The RMI daemon is not running and listening on port 1098 of each remote host.
    3. The necessary java objects have not been successfully registered with each RMI registry.

    Once a remote crawler is launched, you can verify that it is running by one or more of the following methods:

  9. Check for active java processes on the remote crawler host.

    A simple way to confirm that remote crawler is running on the remote crawler host is to use an operating system command such as "ps" on Unix systems. You should look for active java processes.

  10. Monitor the contents of the schedule log file.

    Finally, if the remote crawler is running successfully, you should see the contents of the schedule log file changing periodically. The schedule log file will be located in the shared log directory.