Load balancer tweaks

[levkk]

Description

• Add read_write_split configuration option. If set to include_primary, the primary will be used for read queries. If set to exclude_primary, only replicas will be used for read queries.
• Fix Golang simple protocol with admin database (missing parameter).
• Respond with EmptyQueryResponse when client sends an empty query instead of an error.
• More tests.

[jazzberry-ai]

Bug Report

Incorrect quoting in SET command for enum values.|High|The TestRoundRobinWithPrimary test in integration/go/go_pgx/load_balancer_test.go uses the command SET load_balancing_strategy TO 'round_robin'.|This will result in the value being deserialized as a string containing single quotes, which is incorrect.|

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[Copilot]

Pull Request Overview

A set of updates to introduce and wire up a new read/write split configuration, improve Go simple protocol support, and expand test coverage.

• Add read_write_split config option to direct reads to primary or only replicas, and propagate it through Shard and Cluster.
• Refactor the admin SET command JSON parsing and include the new read_write_split parameter.
• Enhance Go integration tests: fix simple-protocol parameter handling and add new load-balancer tests.

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pgdog/src/net/parameter.rs	Return zero when no mutable params to avoid non-deterministic hash
pgdog/src/net/messages/parameter_status.rs	Add standard_conforming_strings to default parameter status
pgdog/src/config/mod.rs	Introduce ReadWriteSplit enum and default on General
pgdog/src/backend/pool/shard.rs	Wire up rw_split field for read routing
pgdog/src/backend/pool/replicas.rs	Clean up LoadBalancingStrategy imports and match arms
pgdog/src/backend/pool/cluster.rs	Pass rw_split through cluster and shards
pgdog/src/admin/set.rs	Extend SET command for read_write_split and JSON parsing
integration/go/go_pgx/pg_tests_test.go	Fix simple protocol tests to use pgtype.Numeric and assert errors
integration/go/go_pgx/load_balancer_test.go	Add end-to-end load balancer tests for read/write routing
integration/go/go_pgx/go.mod	Bump various Go dependencies

Comments suppressed due to low confidence (2)

pgdog/src/backend/pool/shard.rs:1

• Update this module-level doc comment to mention the new rw_split field and how it affects read routing behavior.

//! A shard is a collection of replicas and a primary.

pgdog/src/net/messages/parameter_status.rs:66

• Consider adding a unit test to verify that standard_conforming_strings appears in the default ParameterStatus list.

ParameterStatus {

[Copilot]

Expand this doc comment to explain the read_write_split option semantics, e.g. whether the primary will be included or excluded for read queries.

Suggested change

	/// Read write split.
	/// Determines whether read queries are split from write queries.
	/// When enabled, read queries may be routed to replicas, while write queries
	/// are always routed to the primary database. The primary database may or may not
	/// be included in the pool of nodes handling read queries, depending on the
	/// specific configuration of the load balancing strategy.

[Copilot]

Add an assert.NoError(t, err) after this query to catch any errors during the admin command execution.

Suggested change

	rows, err := conn.Query(context.Background(), command, pgx.QueryExecModeSimpleProtocol)
	rows, err := conn.Query(context.Background(), command, pgx.QueryExecModeSimpleProtocol)
	assert.NoError(t, err)

[jazzberry-ai]

Bug Report

Name	Severity	Example test case	Description
SHOW STATS reports wrong transaction count	High	Run SHOW STATS after executing queries within a transaction.	The SHOW STATS command reports transaction count as the sum of BEGIN, COMMIT, ROLLBACK, and SELECT queries within a transaction, rather than only the number of transactions.

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[jazzberry-ai]

Bug Report

Name	Severity	Example test case	Description
Missing test case for read_write_split = "include_primary"	Medium	Add a new test case to integration/load_balancer/pgx/read_write_split_test.go that sets read_write_split = "include_primary" in integration/load_balancer/pgdog.toml and verifies that read queries are distributed between the primary and replica servers.	The current integration tests only test the exclude_primary case for the read_write_split configuration option. A test case is needed for the include_primary case to ensure that read queries are correctly distributed between the primary and replica servers when this option is enabled. Without this test case, we cannot be sure that the load balancing is working correctly for include_primary.

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[jazzberry-ai]

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