MongoDB: Add replica set support with automatic failover by matejk · Pull Request #5068 · pocoproject/poco

matejk · 2025-11-27T14:56:58Z

Summary

This PR adds comprehensive MongoDB replica set support to the Poco MongoDB library, implementing automatic server discovery, topology monitoring, failover handling, and read preference-based server selection.

New Features

Replica Set Connection Management

ReplicaSetConnection: Wrapper around Connection that provides automatic retry and failover for replica set operations.
ReplicaSetPoolableConnectionFactory: Connection pooling support for replica sets.

Topology Discovery and Monitoring

TopologyDescription: Tracks the state of all servers in a replica set.
ServerDescription: Represents the state of individual MongoDB servers.
TopologyChangeNotification: Notification mechanism for topology changes.

Read Preference Support

ReadPreference: Configures read preference mode (Primary, PrimaryPreferred, Secondary, SecondaryPreferred, Nearest).
Support for tag sets and max staleness constraints.

MongoDB URI Parsing

ReplicaSetURI: Parses and generates MongoDB connection strings.

OpMsgCursor Enhancement

Added support for ReplicaSetConnection in OpMsgCursor.

Known Limitations

No RTT-based server selection: The Nearest read preference selects any available member but does not use RTT for latency-based selection.
See README-ReplicaSet.md for full list of SDAM specification gaps.

Improvements

Use C++ standard library mutex primitives instead of Poco equivalents
Support for IPv6 addresses in replica set configurations
Removed support for pre-5.1 MongoDB (legacy wire protocol)
Prevent duplicate entries in MongoDB::Document
SSL socket factory support for secure connections

Fixes

Fixed parsing of MongoDB replica set URIs
Changed heartbeatFrequency to heartbeatFrequencyMS to match MongoDB specification
Prevent servers from different replica sets being used in the same topology

Documentation and Samples

Added comprehensive README-ReplicaSet.md documentation
New samples: ReplicaSet.cpp, ReplicaSetMonitor.cpp, URIExample.cpp

Tests

New BSONTest suite with comprehensive BSON serialization tests
New ReplicaSetTest suite covering URI parsing, topology discovery, server selection, and failover scenarios

CI/Build

Speed up CI builds with cmake --build --parallel 4
Upgrade CodeQL from v3 to v4
Fix C++ modules build

MongoDB/src/ReplicaSetConnection.cpp

MongoDB/src/TopologyDescription.cpp

MongoDB/testsuite/src/BSONTest.cpp

aleks-f · 2025-12-06T00:37:03Z

@matejk you have fix for failing odbc CI in main

…osts from "hello" only to discover replica set hosts.

…n and pool.

…. Use notification instead.

…andard URL

…scovered servers.

MongoDB/src/TopologyDescription.cpp

…n the topology.

MongoDB/src/TopologyDescription.cpp

https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/

enh(MongoDB): Remove dead code and mark Message as implementation detail. enh(CI): Fix build of C++ modules

matejk self-assigned this Nov 27, 2025

matejk added the feature label Nov 27, 2025

matejk changed the title ~~Mongodb replica set support~~ MongoDB replica set support Nov 27, 2025

github-advanced-security bot found potential problems Nov 27, 2025

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MongoDB/src/TopologyDescription.cpp Fixed Show fixed Hide fixed

MongoDB/src/TopologyDescription.cpp Fixed Show fixed Hide fixed

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MongoDB/testsuite/src/BSONTest.cpp Fixed Show fixed Hide fixed

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matejk force-pushed the mongodb-replica-set-support branch from b572b42 to 7673ae9 Compare December 4, 2025 13:38

matejk added this to the Release 1.15.0 milestone Dec 5, 2025

matejk force-pushed the mongodb-replica-set-support branch from cd8bbb1 to bd123a2 Compare December 8, 2025 15:55

matejk added 20 commits December 9, 2025 07:14

feature(MongoDB): Initial implementation of support for replica sets.

04f554a

enh(MongoDB): Add parsing of mongodb replica set URI.

459981e

enh(MongoDB): Treat single-server as primary, fix parsing of URI.

3cfcb9b

fix(MongoDB): Add missing example for parsing the URI.

49edbd0

enh(MongoDB): simplified and modernised code.

23a07da

fix(MongoDB): Fixes based on static analysis report.

9bc538d

enh(MongoDB): Remove unused includes.

67d5374

fix(MongoDB): ReplicaSetMonitor: handle wrong arguments more gracefully.

2cb3b4b

enh(MongoDB) Use string literals and char constants where possible.

18de3eb

enh(MongoDB) More tests.

b43264b

fix(MongoDB): Prevent duplicate entries in MongoDB::Document.

64c4071

enh(MongoDB): Update RS tests, remove support for pre 5.1 MongoDB.

3c6fef3

enh(MongoDB): Use C++ std mutex primitives instead of Poco.

88e6146

fix(MongoDB): correct replica set compile errors.

8dad4c8

fix(MongoDB): fix replica set tests to work with IPv6 addresses.

f8662a1

enh(MongoDB): Remove confusing hosts from ServerDescription and use h…

c3de7eb

…osts from "hello" only to discover replica set hosts.

enh(MongoDB): fix unused variables in tests.

449e3c7

enh(MongoDB): Add read-preference validation to replica set connectio…

c284666

…n and pool.

chore(MongoDB): Add reserve to Document.

cefb826

enh(MongoDB): connect to server in pool activateObject.

1a597cd

matejk added 8 commits December 9, 2025 07:14

enh(MongoDB): Replica set: send notification on topology change.

d493b2a

enh(MongoDB): Replica set: Remove internal logger for

840d86f

enh(MongoDB): Replica set: Remove internal logger for topology change…

037e65e

…. Use notification instead.

enh(MongoDB): Update samples and replica set readme.

77e64df

enh(MongoDB): Fix parsing replica set URI.

56f2069

enh(MongoDB): Introduce ReplicaSetURI for handling custom URI.

3f409c7

fix(MongoDB): heartbeatFrequency --> heartbeatFrequencyMS to match st…

9c22e96

…andard URL

enh(MongoDB): Introduce constants in ReplicaSetURI.

fda7d81

matejk force-pushed the mongodb-replica-set-support branch from 3ecb2ea to fda7d81 Compare December 9, 2025 06:14

chore(MongoDB): Minor enhancements.

6303310

matejk added breaking A breaking change performance labels Dec 10, 2025

matejk marked this pull request as ready for review December 10, 2025 12:29

enh(MongoDB): Correct logic to determine replica set topology from di…

c88efc0

…scovered servers.

matejk requested a review from aleks-f December 10, 2025 14:43

github-advanced-security bot found potential problems Dec 10, 2025

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MongoDB/src/TopologyDescription.cpp Dismissed Show dismissed Hide dismissed

MongoDB/src/TopologyDescription.cpp Dismissed Show dismissed Hide dismissed

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matejk added 4 commits December 10, 2025 16:05

enh(MongoDB): Remove redundant code when parsing hello response.

0a44b32

enh(MongoDB): Prevent servers from different replica set to be used i…

306d015

…n the topology.

enh(MongoDB): Mark topology with incompatible servers as Unknown.

d7222a4

enh(CI): Speed-up build by using cmake --build --parallel 4

f192c6e

github-advanced-security bot found potential problems Dec 10, 2025

View reviewed changes

enh(CI): Upgrade codeql from v3 to v4

50466f4

https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/

matejk force-pushed the mongodb-replica-set-support branch from baf85a2 to 50466f4 Compare December 11, 2025 23:31

matejk added 2 commits December 12, 2025 10:45

enh(modules): Update MongoDB module to reflect latest state.

2d436d0

enh(MongoDB): Remove dead code and mark Message as implementation detail. enh(CI): Fix build of C++ modules

fix(C++ modules): Use C++20 features in samples, not C++23.

1b83973

matejk force-pushed the mongodb-replica-set-support branch from 875ffcd to 1b83973 Compare December 12, 2025 10:00

docs(MongoDB): Clarify RTT limitation in Nearest read preference

82258d8

matejk merged commit 51f3749 into main Dec 16, 2025
75 checks passed

matejk deleted the mongodb-replica-set-support branch December 16, 2025 06:49

matejk changed the title ~~MongoDB replica set support~~ MongoDB: Add replica set support with automatic failover Dec 20, 2025

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matejk commented Nov 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

New Features

Replica Set Connection Management

Topology Discovery and Monitoring

Read Preference Support

MongoDB URI Parsing

OpMsgCursor Enhancement

Known Limitations

Improvements

Fixes

Documentation and Samples

Tests

CI/Build

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aleks-f commented Dec 6, 2025

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matejk commented Nov 27, 2025 •

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