PostgresSQL Replication Slot Component

Available as of Camel version 3.0

This is a component for Apache Camel which allows for consuming from PostgreSQL replication slots. The component works with PostgreSQL 10 or later.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-pg-replication-slot</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

The pg-replication-slot component uses the following two styles of endpoint URI notation:

pg-replication-slot://host:port/database/slot:plugin[?parameters]

You can append query options to the URI in the following format, ?option=value&option=value&…​

Options

The PostgresSQL Replication Slot component supports 1 options, which are listed below.

Name Description Default Type

basicPropertyBinding (advanced)

Whether the component should use basic property binding (Camel 2.x) or the newer property binding with additional capabilities

false

boolean

The PostgresSQL Replication Slot endpoint is configured using URI syntax:

pg-replication-slot:host:port/database/slot:outputPlugin

with the following path and query parameters:

Path Parameters (5 parameters):

Name Description Default Type

slot

Required Replication slot name.

String

host

PostgreSQL server host

localhost

String

port

PostgreSQL server port

5432

Integer

database

Required PostgreSQL database name

String

outputPlugin

Required Output plugin name (e.g. test_decoding, wal2json)

String

Query Parameters (25 parameters):

Name Description Default Type

password (common)

PostgreSQL password

String

user (common)

PostgreSQL username

postgres

String

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

sendEmptyMessageWhenIdle (consumer)

If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead.

false

boolean

exceptionHandler (consumer)

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.

ExceptionHandler

exchangePattern (consumer)

Sets the exchange pattern when the consumer creates an exchange.

ExchangePattern

pollStrategy (consumer)

A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel.

PollingConsumerPollStrategy

autoCreateSlot (advanced)

Auto create slot if it does not exist

true

Boolean

basicPropertyBinding (advanced)

Whether the endpoint should use basic property binding (Camel 2.x) or the newer property binding with additional capabilities

false

boolean

slotOptions (advanced)

Slot options to be passed to the output plugin.

Map

statusInterval (advanced)

Specifies the number of seconds between status packets sent back to Postgres server.

10

Integer

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

backoffErrorThreshold (scheduler)

The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in.

int

backoffIdleThreshold (scheduler)

The number of subsequent idle polls that should happen before the backoffMultipler should kick-in.

int

backoffMultiplier (scheduler)

To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the next actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured.

int

delay (scheduler)

Milliseconds before the next poll. You can also specify time values using units, such as 60s (60 seconds), 5m30s (5 minutes and 30 seconds), and 1h (1 hour).

500

long

greedy (scheduler)

If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the previous run polled 1 or more messages.

false

boolean

initialDelay (scheduler)

Milliseconds before the first poll starts. You can also specify time values using units, such as 60s (60 seconds), 5m30s (5 minutes and 30 seconds), and 1h (1 hour).

1000

long

runLoggingLevel (scheduler)

The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that.

TRACE

LoggingLevel

scheduledExecutorService (scheduler)

Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool.

ScheduledExecutorService

scheduler (scheduler)

To use a cron scheduler from either camel-spring or camel-quartz component

none

String

schedulerProperties (scheduler)

To configure additional properties when using a custom scheduler or any of the Quartz, Spring based scheduler.

Map

startScheduler (scheduler)

Whether the scheduler should be auto started.

true

boolean

timeUnit (scheduler)

Time unit for initialDelay and delay options.

MILLISECONDS

TimeUnit

useFixedDelay (scheduler)

Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details.

true

boolean

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-pg-replication-slot-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 2 options, which are listed below.

Name Description Default Type

camel.component.pg-replication-slot.basic-property-binding

Whether the component should use basic property binding (Camel 2.x) or the newer property binding with additional capabilities

false

Boolean

camel.component.pg-replication-slot.enabled

Enable pg-replication-slot component

true

Boolean

Example

from("pg-replication-slot://localhost:5432/finance/sync_slot:test_decoding?user={{username}}&password={{password}}&slotOptions.skip-empty-xacts=true&slotOptions.include-xids=false")
    .to("mock:result");

Tips

PostgreSQL can generate a huge amount of empty transactions on certain operations (e.g. VACUUM). These transactions can congest your route. Using greedy=true query parameter can help with this problem. It will help your route filter out empty transactions quickly without waiting for the delay*timeUnit parameter between each exchange.
The order of the messages is guaranteed, but the same message might come more than once. So, for example, if you’re using this component to sync data from PostgreSQL to other database, make sure your operations are idempotent (e.g. use UPSERT instead of INSERT,…​). This will make sure repeated messages won’t affect your system negatively.