Query Table Replication Sample

The Query Table Replication sample shows StreamBase automatic table replication, as well as customized table replication using table delta streams. There are two parts to the sample: a basic sample and custom sample.

  • The basic sample is set of applications and scripts where automatic table replication is enabled.

  • The custom sample is similar, except that it does not enable automatic table replication. Instead it uses a module reference to monitor HA leadership status of the servers. The purpose of the custom sample is to show details to help you customize leadership control to meet your own requirements.

The behavior of the two samples when you run them is the same, except for the specifics of the table replication process.

The samples specify stream-to-stream connections between containers running on separate StreamBase Servers. Both samples make use of the StreamBase automatic high-availability feature.

Note

You might find it useful to read about the use of automatic high availability in High Availability Sample before proceeding with the table replication samples.

Overview

Each sample runs a simple application on each of two server instances. At any given time, one server is designated as primary, and the other is designated as secondary. On startup, the primary server is designated as leader, and the secondary is designated as nonleader. The servers coordinate their behavior to provide high-availability access to the sample application's Query Table.

When you enable automatic table replication, as in the basic sample, StreamBase handles the coordination and replication process internally. If automatic table replication is not enabled, as in the custom sample, high availability is handled internally as in the basic sample, but table replication is accomplished by means of additional StreamBase modules.

The sample provides the following kinds of files:

  • orders applications

    Provide a very simple example of using a Query Table. You can think of this Query Table as the orders table.

  • table schema definition modules

    Provide table schemas imported by the orders applications. (These are StreamSQL files.)

  • replication modules

    The replication modules are used only in the custom sample, and they are designed to show how you can customize the table replication process instead of relying on the automatic process. (The replication modules are named with _SB_ as a prefix, as in _SB_repl.sbapp.)

  • scripts

    There is a set of scripts for the basic sample, and another set for the custom sample. There is also a script used by both the basic and custom scripts. The startup scripts set environment variables, start the primary server, start the secondary server, start a feed simulation, and start a dequeue from all streams.

  • configuration files

    In addition to sbd.sbconf, there are server configuration files for the basic and custom HA servers. It is important to note the <table-replication> section of these files as part of understanding table replication.

Updates to Replication Tables

The orders modules on both the leader and the nonleader have identical Query Tables, which import ReplTableInterface as a StreamBase table schema. The design pattern of both samples is intended to meet the following requirements:

  • Any nonleader has the ability to create a replica of the orders table if necessary.

  • A module on a new server connecting to the cluster can become the leader if necessary.

Each orders table is maintained as ReplTable. There are two kinds of updates to the replication tables:

Bulk requests

Bulk requests are requests from the nonleader to the leader for a range of table updates. The purpose of bulk requests is to get the nonleader caught up after a network partition, or during initial startup.

Real time updates

Real time updates are table updates that are sent from the leader to the nonleader during normal real time operation. If the nonleader is processing bulk requests it ignores these updates and gets caught up eventually using bulk requests.

On the leader, each change to the orders table causes the corresponding change in the orders table on the nonleader.

Applications

The sample_table-repl/apps directory has the applications for both basic and custom samples, as follows:

  • orders.sbapp (automatic table replication is enabled)

  • ordersImports.ssql (defines table schema imported by orders.sbapp)

  • orders-custom.sbapp (automatic table replication is not enabled)

  • orders-customImports.ssql (defines table schema imported by orders-custom.sbapp)

  • _SB_repl.sbapp and other _SB_ files (monitors and handles table replication when automatic table replication is not enabled)

Understanding the Basic Sample

The orders application is a basic example of a high-availability design that uses both automatic high availability and automatic table replication. This application runs on each server in the high-availability pair. It consumes orders data and determines if its containing server is the leader. If it is the leader, it updates the orders table on its containing server, and StreamBase Server takes care of updating the Query Table on the nonleader.

Table replication has been enabled as a property of the orders table, as shown:

In addition, the server configuration file (orders.sbconf) includes the following element as part of the <high-availability> section:

<table-replication>
  <!-- HB_OTHER_SERVER: The host name of the other server -->
  <param name="HB_OTHER_SERVER" value="${HB_OTHER_SERVER}"/>

  <!-- REPL_OTHER_SERVER_PORT: The sbd port on the other host
       participating in table replication -->
  <param name="REPL_OTHER_SERVER_PORT" value="${REPL_OTHER_SERVER_PORT}"/>

  <!-- REPL_CHECK_INTERVAL: Optional parameter (in seconds) which defines
       how often do we check the replication state of the table -->
  <param name="REPL_CHECK_INTERVAL" value="1"/>

  <!-- REPL_BATCH_SIZE: Optional parameter which defines how big the batches
       (in tuples) that are sent from the LEADER to the NON_LEADER -->
  <param name="REPL_BATCH_SIZE" value="${REPL_BATCH_SIZE}"/>

  <!-- REPL_RECONNECT_INTERVAL: Optional parameter which defines how often
       (in milliseconds) that reconnects are attempted between the LEADER and 
       NON_LEADER -->
  <param name="REPL_RECONNECT_INTERVAL" value="250"/>
</table-replication>

Understanding the Custom Sample

Like orders.app, the orders-custom.sbapp application uses automatic high-availability to monitor and control leadership status between a pair of servers. This application differs from orders.sbapp in the way it handles table replication as follows:

  • _SB_delta_ReplTable is a table delta stream associated with ReplTable, the orders table

  • _SB_repl.sbapp is a module reference that handles table replication using the table delta stream.

When the nonleader starts up, its orders table is empty. At startup, the replication module (_SB_repl.sbapp) on the nonleader does the following:

  • Attempts to get a bulk entry update from the leader. Real-time updates are ignored while bulk updates are being requested or processed.

  • On intervals of one second, a metronome is fired to ensure that the nonleader is up to date.

  • If the nonleader is not up to date (which is the case on startup), the replication module initiates a bulk entry request to the leader. This request copies entries from the orders table in batches to avoid overwhelming resources such as the server or the network.

  • When the batch update is complete, new orders events are processed in real time by means of a table delta stream.

The replication module uses timeouts to guard against network failures, and it is designed to be resilient if the network fails.

The replication module cannot determine if the container connections are active. If these connections disconnect, the replication module continues to send bulk replication requests on a specified interval.

Environment Variables

The following table lists all the environment variables that must be set for the samples to run. The scripts in the sample have settings for the environment variables. If you develop another application based on the applications in the sample, be sure to set the environment variables as required to run the new application.

Environment Variable Refers to
APP File name of the application to run.
APPSDIR Directory where the HA applications are located
APP_CONTAINER Container name for the container for APP
HB_PORT Port number for the HA HeartBeat adapter on the other server in a high-availability pair (must be the same value for both servers).
HB_OTHER_SERVER Hostname of the server for the paired StreamBase Server.
INITIAL_LEADERSHIP_STATUS The initial leadership status of the server. Usually the server that starts first is the leader and others are nonleaders.
SBD_PORT Port number to be used by the server. The servers must have different values.
REPL_OTHER_SERVER_PORT Hostname of the other server in the pair of HA servers.

This Sample's Files

The folders and files delivered with the Query Table Replication sample are as follows:

Sample Directory Contains
table-repl

The top level directory of the sample contains:

common

UNIX shell script shared by basic and custom scripts.

common.cmd

Windows script shared by basic and custom scripts.

orders-custom.sbconf

Server configuration file used by the custom scripts.

orders.sbconf

Server configuration file used by the basic scripts.

sbd.sbconf

Server configuration file used by Studio for typechecking only.

apps

Contains all of the EventFlow and StreamSQL application files:

orders.sbapp

Orders application used by the basic setup. Automatic table replication is enabled.

ordersImports.ssql

Import file for the orders application.

orders-custom.sbapp

Orders application used by the custom setup. Table replication is set up manually.

orders-customImports.ssql

Import file for the orders-custom application.

Files with a prefix of _SB_ are used by the table replication infrastructure to replicate tables. Note that some of files are EventFlow modules and some are StreamSQL modules. This is because some operations are better performed in one or the other.

_SB_replCreateGapDeltaTuple.sbapp

Application used to create a gap tuple if needed.

_SB_replImports.ssql

Import file used mostly for typechecking. The table replication applications depend on the configuration file orders-custom.sbconf.

_SB_replQueueConstants.ssql

Import file that contains constants for the queue application.

_SB_replQueue.ssql

An application that creates a queue for delta tuples that arrive while we are doing bulk loading.

_SB_repl.sbapp

The main table replication application. Container connection URI strings are specified on the Advanced tab of the Properties view for the three primary input streams. These connection URIs include the parameter ConnectOnInit=false which prevents the container connection from blocking the startup of the containing StreamBase Server. See Remote Container Connection Parameters for details.

_SB_replTableOperations.ssql

This file contains operations that are performed on the replicated table.

basic-scripts

Scripts to run the sample using the basic HA setup and automatic table replication. In this part of the sample, the server does the work of table replication.

basic-common

UNIX shell script shared by all the UNIX scripts in basic-scripts.

basic-common.cmd

Windows script shared by all the Windows scripts in basic-scripts.

startdequeue, startdequeue.cmd

UNIX shell script and Windows script used to dequeue from the app container.

startfeedsim, startfeedsim.cmd

UNIX shell script and Windows script used to start sbfeedsim to send data into the app container. Runs the sbfeedsim command with a comma-separated double URI syntax that addresses both primary and secondary servers at the same time. This starts a feed simulation based on the schema of the orders.sbapp application, and begins feeding generated values to both servers.

startprimary, startprimary.cmd

UNIX shell script and Windows script used to start the primary server as LEADER.

startprimaryasnonleader, startprimaryasnonleader.cmd

UNIX shell script and Windows script used to restart the primary server as NON_LEADER. Useful for restarting a server that was originally the primary but shut down and should not be leader when it starts again.

startsecondary, startsecondary.cmd

UNIX shell script and Windows script used to start the secondary server as NON_LEADER.

custom-scripts

Scripts to run the sample using the basic HA setup and a custom table replication setup. The custom sample shows how to manually create a table replication design pattern.

custom-common

UNIX shell script shared by all the UNIX scripts in custom-scripts.

custom-common.cmd

Windows script shared by all the Windows scripts in custom-scripts.

startdequeue, startdequeue.cmd

UNIX shell script and Windows script used to dequeue from the app container. Runs sbc dequeue with the comma-separated double URI syntax, which begins dequeuing from both servers at the same time. However, only the server designated as leader is processing tuples to be dequeued.

startfeedsim, startfeedsim.cmd

UNIX shell script and Windows script used to start sbfeedsim to send data into the app container. Runs the sbfeedsim command with a comma-separated double URI syntax that addresses both primary and secondary servers at the same time. This starts a feed simulation based on the schema of the custom-orders.sbapp application, and begins feeding generated values to both servers.

startprimary, startprimary.cmd

UNIX shell script and Windows script used to start the primary server as LEADER.

startprimaryasnonleader, startprimaryasnonleader.cmd

UNIX shell script and Windows script used to start the primary server as NON_LEADER. Useful for restarting a server that was originally the primary but shut down and should not be leader when it starts again.

startsecondary, startsecondary.cmd

UNIX shell script and Windows script used to start the secondary server as NON_LEADER.

Exploring the Sample Applications in StreamBase Studio

This sample is designed to run in UNIX terminal windows or Windows StreamBase Command Prompt windows, because StreamBase Studio cannot run more than one instance of a server. Nonetheless, it is recommended that you open the application files in StreamBase Studio to study how the applications are assembled. For an introduction to the design of the sample, see the overview at the top of this document.

Running This Sample with StreamBase Authentication

The table-repl sample is shipped with support for StreamBase authentication disabled. To run this sample with StreamBase authentication enabled, you must perform the following prerequisite steps:

  1. Create an authentication database, usually stored in $STREAMBASE_HOME/etc, using the sbuseradmin command. For instructions, see Using StreamBase Server Simple Authentication.

  2. In the authentication database, create at least one StreamBase username with the SBAdmin role.

  3. Set the following environment variables:

    AUTH true
    AUTH_PASSWORD_FILE Path to the authentication password file created with sbuseradmin.
    AUTH_ADMINUSER Username assigned the SBAdmin role in the authentication file.
    AUTH_ADMINPASSWORD Password for the above username.

    These variables apply to the HA family of samples, and are not StreamBase standard environment variables.

Running This Sample in Terminal Windows

This section shows how to get the sample running and suggests some steps to show how the servers and the applications work together to ensure high availability. You can, of course, try out other steps of your own, and also use the sample as a starting point for a design pattern that meets your particular requirements.

To get the sample up and running you use scripts that do the following:

  • Start the servers.

  • Start a feed simulation to all streams.

  • Start a dequeue from all streams.

After the sample is running, you can test the high-availability features by entering some data and observing that the Query Tables on both servers are exactly the same.

Because StreamBase Studio can run only one server instance at a time, you must run the two servers in the Query Table Replication sample in terminal or StreamBase Command Prompt windows.

Note

On Windows, be sure to use the StreamBase Command Prompt from the Start menu, not the Windows command prompt.

Step by Step Instructions to Run the Sample

The steps to run the sample are as follows:

  1. Set up five terminal windows.

    1. Open five terminal windows on UNIX, or five StreamBase Command Prompt s on Windows.

    2. In each window, navigate your Studio workspace copy of the sample.

      Note

      Note that there are two sets of scripts in two separate folders: basic-scripts and custom-scripts. To run each of the two samples, navigate first to the basic scripts folder, follow the steps for running the sample, then navigate to the custom scripts folder and repeat the steps.

  2. Start the following processes:

    1. In window 1, start the first server with this command: startprimary.

      This script starts a server listening on port 9900 and loads the high availability application (ha) in a container, ha, on that server. The high availability application designates this server as the leader, sets up the required ports, including HB_PORT for the HA Heartbeat adapter, and starts app.

    2. In window 2, run startsecondary.

      This script is the same as startprimary except that it starts a server listening on port 9901 and designates this server as the nonleader. Observe that at this point the servers are connected and listening.

    3. In window 3, run startfeedsim.

      A feed simulation starts sending input data to both servers on OrdersIn, an input stream in orders.sbapp.

    4. In window 4, run startdequeue.

      Dequeuing from orders.sbapp begins, including dequeuing from _SB_repl.sbapp (named TableReplication in the sample).

  3. Observe the high availability process by terminating the server in window 1.

    1. In window 5, run the following command:

      sbadmin -p 9900 shutdown

      In window 1 the server shuts down.

    2. In window 5, enter the command:

      sbadmin getLeadershipStatus

      Notice that the server on port 9901, which is running in window 2, has become the leader.

    3. In window 3 notice that the feed simulation continues to enqueue.

    4. In window 4, notice that dequeuing has continued.

  4. Observe the replication process by sending data to the orders application and observing the Query Table before and after the leader stops running.

    1. Start the sample again:

      1. Terminate the processes in windows 1, 2, 3, and 4 by pressing Ctrl+C.

      2. Start the servers again by running startprimary in window 1 and startsecondary in window 2.

      3. In window 3, run sbfeedsim as before, but terminate it shortly after it starts. This step inserts a few rows into ReplTable on each server.

      At this point, the only processes running are in windows 1 and 2, and the leader is running in window 1.

    2. In window 4, start a dequeuer for the data from the GetAllOrdersOut stream on the leader as shown:

      sbc -p 9900 dequeue app.GetAllOrdersOut

      No tuples are dequeued yet.

    3. In window 3, instead of running the feed simulation, enter some data manually. The GetAllOrdersIn stream in orders.sbapp has a single field of data type integer. You can enqueue any integer value for this field.

      Type the following command to start enqueuing:

      sbc -p 9900 enqueue app.GetAllOrdersIn

      Then type any integer as the value, such as:

      123
    4. In window 4, observe that the results from enqueued data are displayed as rows similar to the following:

      TGQO,1,5975.45277797202,IKZW
      YHDD,2,232.381224838895,OZCQ
      KUZM,3,7462.41405322331,TVVN
      XDCZ,4,7223.57119188849,SDMA
      BJIW,5,9715.46988851713,WPEF
    5. In window 1, shut down the leader by ending the process, and observe that window 2 becomes the leader.

    6. In window 5, start a dequeuer for the data from the GetAllOrdersOut stream on the new leader as shown:

      sbc -p 9901 dequeue app.GetAllOrdersOut
    7. In window 3, stop the enqueuing to 9900 and enter some data manually to the new leader.

      sbc -p 9901 enqueue app.GetAllOrdersIn 
      456

      The data from ReplTable is displayed in window 5. Observe that the data is exactly the same as the data in window 4. That is, the Query Table on the new leader is a replica of the Query Table on the leader before it was shut down.

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Importing This Sample into StreamBase Studio

In StreamBase Studio, import this sample with the following steps:

  • From the top menu, select FileLoad StreamBase Sample.

  • Select table-repl from the High Availability list.

  • Click OK.

StreamBase Studio creates a single project containing the sample files. The default project name is sample_table-repl.

Sample Location

When you load the sample into StreamBase Studio, Studio copies the sample project's files to your Studio workspace, which is normally part of your home directory, with full access rights.

Important

Load this sample in StreamBase Studio, and thereafter use the Studio workspace copy of the sample to run and test it, even when running from the command prompt.

Using the workspace copy of the sample avoids permission problems. The default workspace location for this sample is:

studio-workspace/sample_table-repl

See Default Installation Directories for the location of studio-workspace on your system.

In the default TIBCO StreamBase installation, this sample's files are initially installed in:

streambase-install-dir/sample/table-repl

See Default Installation Directories for the default location of studio-workspace on your system.