NPipeline.Connectors.PostgreSQL

A PostgreSQL connector for NPipeline data pipelines. Provides source and sink nodes for reading from and writing to PostgreSQL databases with support for multiple write strategies, upsert operations, delivery semantics, checkpointing, convention-based mapping, custom mappers, connection pooling, and streaming.

Installation

dotnet add package NPipeline.Connectors.PostgreSQL

Quick Start

Reading from PostgreSQL

using NPipeline.Connectors.PostgreSQL; using NPipeline.Pipeline; // Define your model public record Customer(int Id, string Name, string Email); // Create a source node var connectionString = "Host=localhost;Database=mydb;Username=postgres;Password=password"; var source = new PostgresSourceNode<Customer>( connectionString, "SELECT id, name, email FROM customers" ); // Use in a pipeline var pipeline = new PipelineBuilder() .AddSource(source, "customer_source") .AddSink<ConsoleSinkNode<Customer>, Customer>("console_sink") .Build(); await pipeline.RunAsync();

Writing to PostgreSQL

using NPipeline.Connectors.PostgreSQL; using NPipeline.Pipeline; // Define your model public record Customer(int Id, string Name, string Email); // Create a sink node var connectionString = "Host=localhost;Database=mydb;Username=postgres;Password=password"; var sink = new PostgresSinkNode<Customer>( connectionString, "customers", writeStrategy: PostgresWriteStrategy.Batch ); // Use in a pipeline var pipeline = new PipelineBuilder() .AddSource<InMemorySourceNode<Customer>, Customer>("source") .AddSink(sink, "customer_sink") .Build(); await pipeline.RunAsync();

Using StorageUri for Environment-Aware Configuration

The PostgreSQL connector supports URI-based configuration through StorageUri, enabling seamless environment switching without code changes.

Basic Usage

using NPipeline.Connectors; using NPipeline.Connectors.PostgreSQL; var uri = StorageUri.Parse("postgres://localhost:5432/mydb?username=postgres&password=password"); var source = new PostgresSourceNode<Customer>(uri, "SELECT * FROM customers"); var sink = new PostgresSinkNode<Customer>(uri, "customers");

Environment Switching Example

// Development (local database) var devUri = StorageUri.Parse("postgres://localhost:5432/mydb?username=postgres&password=devpass"); // Production (AWS RDS) var prodUri = StorageUri.Parse("postgres://mydb.prod.ap-southeast-2.rds.amazonaws.com:5432/mydb?username=produser&password=${DB_PASSWORD}"); // Same pipeline code works in both environments var uri = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") == "Production" ? prodUri : devUri; var source = new PostgresSourceNode<Customer>(uri, "SELECT * FROM customers");

URI Parameters

Supported query parameters for PostgreSQL URIs:

Parameter	Type	Description
username	string	Database username
password	string	Database password
sslmode	string	SSL mode: disable, allow, prefer, require, verify-ca, verify-full
timeout	int	Connection timeout in seconds
pooling	bool	Enable connection pooling (true/false)

Using the Resolver Factory

using NPipeline.Connectors.Abstractions; using NPipeline.Connectors.PostgreSQL; var resolver = PostgresStorageResolverFactory.CreateResolver(); var uri = StorageUri.Parse("postgres://localhost:5432/mydb?username=postgres&password=password"); // Provider is resolved automatically var provider = resolver.ResolveProvider(uri); var connectionString = ((IDatabaseStorageProvider)provider).GetConnectionString(uri);

Key Features

• Streaming reads - Process large result sets with minimal memory usage
• Multiple write strategies - Per-row, batched inserts, and high-performance COPY protocol
• Upsert support - ON CONFLICT DO UPDATE / ON CONFLICT DO NOTHING SQL generation
• Delivery semantics - At-least-once, at-most-once, and exactly-once delivery guarantees
• Checkpointing strategies - InMemory, Offset, KeyBased, Cursor, and CDC checkpointing
• Connection pooling - Efficient connection management via dependency injection
• Convention-based mapping - Automatic PascalCase to snake_case conversion
• Custom mappers - Full control over row-to-object mapping
• Retry logic - Automatic retry for transient errors
• SSL/TLS support - Secure database connections
• SQL injection prevention - Identifier validation enabled by default
• Binary COPY support - High-performance binary format for bulk loading

Configuration

PostgresConfiguration

Configure connector behavior with PostgresConfiguration:

var configuration = new PostgresConfiguration { ConnectionString = "Host=localhost;Database=mydb;Username=postgres;Password=password", Schema = "public", StreamResults = true, FetchSize = 1_000, BatchSize = 1_000, MaxBatchSize = 5_000, UseTransaction = true, WriteStrategy = PostgresWriteStrategy.Batch, UseUpsert = false, UseBinaryCopy = false, DeliverySemantic = DeliverySemantic.AtLeastOnce, CheckpointStrategy = CheckpointStrategy.None, MaxRetryAttempts = 3, RetryDelay = TimeSpan.FromSeconds(1), ValidateIdentifiers = true, CommandTimeout = 30, CopyTimeout = 300 };

Configuration Properties

Property	Type	Default	Description
ConnectionString	string	""	PostgreSQL connection string
Schema	string	"public"	Default schema name
WriteStrategy	PostgresWriteStrategy	Batch	Write strategy (PerRow, Batch, Copy)
BatchSize	int	1000	Target batch size for batched writes
MaxBatchSize	int	5000	Maximum batch size to prevent unbounded memory
UseTransaction	bool	true	Wrap writes in a transaction
UseUpsert	bool	false	Enable ON CONFLICT upsert semantics
UpsertConflictColumns	string[]?	null	Columns that form the conflict target
OnConflictAction	OnConflictAction	Update	Conflict resolution action (Update, Ignore)
UseBinaryCopy	bool	false	Use binary format for COPY operations
DeliverySemantic	DeliverySemantic	AtLeastOnce	Delivery guarantee semantic
CheckpointStrategy	CheckpointStrategy	None	Checkpointing strategy for recovery
CheckpointStorage	ICheckpointStorage?	null	Storage backend for checkpoints
StreamResults	bool	true	Enable streaming for large result sets
FetchSize	int	1000	Rows to fetch per round-trip when streaming
CommandTimeout	int	30	Command timeout in seconds
CopyTimeout	int	300	COPY operation timeout in seconds
MaxRetryAttempts	int	3	Maximum retry attempts for transient errors
RetryDelay	TimeSpan	1 second	Delay between retry attempts
ValidateIdentifiers	bool	true	Validate SQL identifiers to prevent injection
UsePreparedStatements	bool	true	Use prepared statements for writes

Connection String

The connection string supports all Npgsql options:

Host=localhost;Port=5432;Database=mydb;Username=postgres;Password=password;Timeout=15;Pooling=true;SslMode=Require

Mapping

Convention-Based Mapping

Properties are automatically mapped to columns using snake_case conversion:

public record Customer( int CustomerId, // Maps to customer_id string FirstName, // Maps to first_name string EmailAddress // Maps to email_address );

Attribute-Based Mapping

Override default mapping with attributes:

using NPipeline.Connectors.PostgreSQL.Mapping; public record Customer( [PostgresColumn("cust_id", PrimaryKey = true)] int Id, [PostgresColumn("full_name")] string Name, [PostgresIgnore] string TemporaryField );

Custom Mappers

For complete control, provide a custom mapper function:

var source = new PostgresSourceNode<Customer>( connectionString, "SELECT id, name, email FROM customers", rowMapper: row => new Customer( row.GetInt32(row.GetOrdinal("id")), row.GetString(row.GetOrdinal("name")), row.GetString(row.GetOrdinal("email")) ) );

Write Strategies

The PostgreSQL connector supports three write strategies, each optimized for different use cases.

PerRow Strategy

Writes each row individually with a separate INSERT statement.

Best for:

• Small batches or real-time processing
• Per-row error handling requirements
• Scenarios where immediate visibility of each row is critical

var sink = new PostgresSinkNode<Customer>( connectionString, "customers", writeStrategy: PostgresWriteStrategy.PerRow );

Trade-offs: Higher overhead for large datasets due to individual round-trips, but provides better error isolation.

Batch Strategy

Buffers rows and issues a single multi-value INSERT statement (e.g., INSERT INTO table VALUES (...), (...), (...)).

Best for:

• Large datasets and bulk imports
• High-throughput scenarios
• Balanced performance and reliability

var configuration = new PostgresConfiguration { BatchSize = 1_000, MaxBatchSize = 5_000, UseTransaction = true }; var sink = new PostgresSinkNode<Customer>( connectionString, "customers", writeStrategy: PostgresWriteStrategy.Batch, configuration: configuration );

Trade-offs: 10-100x faster than PerRow for bulk operations, but all rows in a batch succeed or fail together.

Copy Strategy

Uses PostgreSQL's native COPY protocol for maximum throughput. Supports both text and binary formats.

Best for:

• Maximum throughput bulk loading
• Very large datasets (millions of rows)
• Data warehouse loading scenarios

var configuration = new PostgresConfiguration { CopyTimeout = 600, // 10 minutes for large loads UseBinaryCopy = true // Use binary format for better performance }; var sink = new PostgresSinkNode<Customer>( connectionString, "customers", writeStrategy: PostgresWriteStrategy.Copy, configuration: configuration );

Binary vs Text Format:

• Text format (UseBinaryCopy = false): More compatible, easier to debug
• Binary format (UseBinaryCopy = true): 20-30% faster, more efficient encoding

Trade-offs: Fastest option for large datasets, but bypasses some PostgreSQL processing layers and has limited error granularity.

Write Strategy Comparison

Strategy	Throughput	Latency	Error Isolation	Use Case
PerRow	Low	Low	High	Real-time, small batches
Batch	High	Medium	Medium	Bulk loading, ETL
Copy	Very High	High	Low	Large bulk loads, data warehouse

Upsert Operations

The connector supports PostgreSQL's ON CONFLICT clause for upsert operations, allowing you to insert rows or update them if they already exist.

Basic Upsert Configuration

Enable upsert by setting UseUpsert = true and specifying the conflict columns:

var configuration = new PostgresConfiguration { UseUpsert = true, UpsertConflictColumns = new[] { "id" }, // Primary key or unique constraint columns OnConflictAction = OnConflictAction.Update // Update on conflict }; var sink = new PostgresSinkNode<Customer>( connectionString, "customers", writeStrategy: PostgresWriteStrategy.Batch, configuration: configuration );

Conflict Actions

OnConflictAction.Update

Updates non-conflict columns with values from the inserted row:

INSERT INTO customers (id, name, email) VALUES (1, 'John Doe', 'john@example.com') ON CONFLICT (id) DO UPDATE SET name = EXCLUDED.name, email = EXCLUDED.email var configuration = new PostgresConfiguration { UseUpsert = true, UpsertConflictColumns = new[] { "id" }, OnConflictAction = OnConflictAction.Update };

OnConflictAction.Ignore

Silently skips conflicting rows without raising an error:

INSERT INTO customers (id, name, email) VALUES (1, 'John Doe', 'john@example.com') ON CONFLICT (id) DO NOTHING var configuration = new PostgresConfiguration { UseUpsert = true, UpsertConflictColumns = new[] { "id" }, OnConflictAction = OnConflictAction.Ignore };

Composite Conflict Targets

For tables with composite unique constraints:

public record OrderItem(int OrderId, int ProductId, int Quantity, decimal UnitPrice); var configuration = new PostgresConfiguration { UseUpsert = true, UpsertConflictColumns = new[] { "order_id", "product_id" }, // Composite key OnConflictAction = OnConflictAction.Update }; var sink = new PostgresSinkNode<OrderItem>( connectionString, "order_items", writeStrategy: PostgresWriteStrategy.Batch, configuration: configuration );

Upsert with Write Strategies

Upsert works with all write strategies:

• PerRow: Each row is processed individually with upsert semantics
• Batch: Multi-value INSERT with ON CONFLICT clause
• Copy: Not supported for upsert operations (falls back to Batch)

Why use upsert: Upsert eliminates the need for separate insert/update logic and handles race conditions where a row might be inserted between your check and insert operations.

Delivery Semantics

The connector supports three delivery semantics to control data consistency guarantees during failures.

AtLeastOnce (Default)

Guarantees that every item is delivered at least once. Items may be duplicated on retry after a failure.

var configuration = new PostgresConfiguration { DeliverySemantic = DeliverySemantic.AtLeastOnce, UseTransaction = true };

Characteristics:

• No data loss
• Possible duplicates on retry
• Best for idempotent operations or when duplicates can be tolerated

Use when:

• Processing idempotent operations
• Duplicates can be filtered downstream
• Data loss is unacceptable

AtMostOnce

Guarantees that every item is delivered at most once. Items may be lost on failure, but never duplicated.

var configuration = new PostgresConfiguration { DeliverySemantic = DeliverySemantic.AtMostOnce };

Characteristics:

• No duplicates
• Possible data loss on failure
• Best for high-throughput scenarios where occasional data loss is acceptable

Use when:

• Processing telemetry or metrics data
• High throughput is critical
• Occasional data loss is acceptable

ExactlyOnce

Guarantees that every item is delivered exactly once. Uses transactional semantics to prevent both data loss and duplication.

var configuration = new PostgresConfiguration { DeliverySemantic = DeliverySemantic.ExactlyOnce, UseTransaction = true, CheckpointStrategy = CheckpointStrategy.Offset, CheckpointStorage = new FileCheckpointStorage("checkpoints.json") };

Characteristics:

• No data loss
• No duplicates
• Higher overhead due to transaction coordination
• Requires checkpoint storage

Use when:

• Financial transactions
• Audit logging
• Any scenario requiring strict exactly-once guarantees

Delivery Semantic Comparison

Semantic	Data Loss	Duplicates	Overhead	Use Case
AtLeastOnce	No	Possible	Low	General purpose, idempotent ops
AtMostOnce	Possible	No	Low	Telemetry, metrics
ExactlyOnce	No	No	High	Financial, audit

Checkpointing

Checkpointing enables pipelines to resume from where they left off after a failure, rather than restarting from the beginning.

Checkpoint Strategies

None (Default)

No checkpointing is performed. Failures require restarting from the beginning.

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.None };

InMemory

Stores checkpoint state in memory. Enables recovery from transient failures during a single process execution.

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.InMemory, StreamResults = true }; var source = new PostgresSourceNode<Order>( connectionString, "SELECT * FROM orders ORDER BY id", // ORDER BY is required for checkpointing configuration: configuration );

Limitations: Checkpoint state is lost when the process terminates.

Offset

Persists numeric offset checkpoints to external storage. Tracks position using a monotonically increasing column (e.g., auto-increment ID).

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.Offset, CheckpointOffsetColumn = "id", CheckpointStorage = new FileCheckpointStorage("checkpoints/order_offset.json") }; var source = new PostgresSourceNode<Order>( connectionString, "SELECT * FROM orders WHERE id > @lastCheckpoint ORDER BY id", configuration: configuration );

Requirements:

• Requires CheckpointOffsetColumn to be specified
• Requires CheckpointStorage to persist checkpoints
• Query must include ORDER BY on the offset column

KeyBased

Tracks processed items using composite keys. Useful for tables without a single monotonic column.

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.KeyBased, CheckpointKeyColumns = new[] { "customer_id", "order_date" }, CheckpointStorage = new FileCheckpointStorage("checkpoints/order_keys.json") };

Requirements:

• Requires CheckpointKeyColumns to be specified
• Requires CheckpointStorage to persist checkpoints

Cursor

Tracks cursor position for cursor-based iteration.

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.Cursor, CheckpointStorage = new FileCheckpointStorage("checkpoints/cursor.json") };

CDC (Change Data Capture)

Tracks WAL position for PostgreSQL logical replication. Enables capturing changes from the PostgreSQL write-ahead log.

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.CDC, CdcSlotName = "my_pipeline_slot", CdcPublicationName = "my_publication", CheckpointStorage = new FileCheckpointStorage("checkpoints/cdc.json") };

Requirements:

• Requires CdcSlotName to be specified
• Requires PostgreSQL logical replication to be configured
• Requires appropriate PostgreSQL permissions

Checkpoint Storage

Implement ICheckpointStorage to persist checkpoints to your preferred backend:

public interface ICheckpointStorage { Task<Checkpoint?> LoadAsync(string pipelineId, CancellationToken cancellationToken = default); Task SaveAsync(string pipelineId, Checkpoint checkpoint, CancellationToken cancellationToken = default); }

Built-in implementations:

• FileCheckpointStorage - Stores checkpoints in a JSON file
• InMemoryCheckpointStorage - Stores checkpoints in memory (for testing)

Checkpoint Intervals

Configure how frequently checkpoints are saved:

var configuration = new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.Offset, CheckpointInterval = new CheckpointIntervalConfiguration { RowCount = 10_000, // Save every 10,000 rows TimeInterval = TimeSpan.FromMinutes(5) // Or every 5 minutes, whichever comes first } };

Dependency Injection

Register the connector with dependency injection for production applications:

using Microsoft.Extensions.DependencyInjection; using NPipeline.Connectors.PostgreSQL.DependencyInjection; var services = new ServiceCollection() .AddPostgresConnector(options => { options.DefaultConnectionString = "Host=localhost;Database=mydb;Username=postgres;Password=password"; options.AddOrUpdateConnection("analytics", "Host=localhost;Database=analytics;Username=postgres;Password=postgres"); options.DefaultConfiguration = new PostgresConfiguration { StreamResults = true, FetchSize = 1_000, BatchSize = 1_000 }; }) .BuildServiceProvider(); var pool = services.GetRequiredService<IPostgresConnectionPool>(); var sourceFactory = services.GetRequiredService<PostgresSourceNodeFactory>(); var sinkFactory = services.GetRequiredService<PostgresSinkNodeFactory>();

Using Named Connections

var source = new PostgresSourceNode<Customer>( pool, "SELECT * FROM customers", connectionName: "analytics" );

Streaming

Enable streaming for large result sets to reduce memory usage:

var configuration = new PostgresConfiguration { StreamResults = true, FetchSize = 1_000 }; var source = new PostgresSourceNode<Customer>( connectionString, "SELECT * FROM large_table", configuration: configuration );

Why streaming matters: Without streaming, the entire result set is loaded into memory. Streaming fetches rows in batches, allowing you to process millions of rows without memory issues.

Analyzers

The PostgreSQL connector includes a companion analyzer package that provides compile-time diagnostics to help prevent common mistakes when using checkpointing.

Installation

dotnet add package NPipeline.Connectors.PostgreSQL.Analyzers

NP9501: Checkpointing requires ORDER BY clause

Category: Reliability Default Severity: Warning

When using checkpointing with PostgreSQL source nodes, the SQL query must include an ORDER BY clause on a unique, monotonically increasing column. This ensures consistent row ordering across checkpoint restarts. Without proper ordering, checkpointing may skip rows or process duplicates.

Example

// ❌ Warning: Missing ORDER BY clause var source = new PostgresSourceNode<MyRecord>( connectionString, "SELECT id, name, created_at FROM my_table", configuration: new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.Offset } ); // ✅ Correct: Includes ORDER BY clause var source = new PostgresSourceNode<MyRecord>( connectionString, "SELECT id, name, created_at FROM my_table ORDER BY id", configuration: new PostgresConfiguration { CheckpointStrategy = CheckpointStrategy.Offset } );

Why This Matters

Checkpointing tracks the position of processed rows to enable recovery from failures. Without a consistent ORDER BY clause:

• Data Loss: Rows may be skipped during recovery
• Data Duplication: Rows may be processed multiple times
• Inconsistent State: Checkpoint positions become unreliable

Recommended Ordering Columns

Use a unique, monotonically increasing column such as:

• id (primary key)
• created_at (timestamp)
• updated_at (timestamp)
• timestamp (timestamp column)
• Any auto-incrementing or sequential column

For more details, see the PostgreSQL Analyzer documentation.

Error Handling

Retry Configuration

Configure retries for transient failures:

var configuration = new PostgresConfiguration { MaxRetryAttempts = 3, RetryDelay = TimeSpan.FromSeconds(2) };

Custom Exception Handling

try { await pipeline.RunAsync(); } catch (NpgsqlException ex) when (ex.IsTransient) { // Retry operation await Task.Delay(TimeSpan.FromSeconds(5)); await pipeline.RunAsync(); }

SSL/TLS Configuration

Configure SSL/TLS for secure connections:

var configuration = new PostgresConfiguration { // SSL mode is configured via connection string ConnectionString = "Host=localhost;Database=mydb;Username=postgres;Password=password;SslMode=Require" };

Available SSL modes: Disable, Allow, Prefer, Require, VerifyCa, VerifyFull

Prepared Statements

The connector uses prepared statements by default (UsePreparedStatements = true). Prepared statements:

• Reduce query parsing overhead on the database server
• Improve performance for repeated query patterns (same query, different parameters)
• Provide automatic SQL injection protection

When to Disable Prepared Statements

Consider disabling UsePreparedStatements only for:

• Ad-hoc queries that are dynamically generated and never repeated
• Very complex queries that may not benefit from preparation
• Testing scenarios where you need to debug query generation

Performance Impact

Scenario	Prepared Statements	Performance Impact
Repeated inserts (same query pattern)	Enabled	10-30% faster
Ad-hoc queries (different each time)	Enabled	5-10% overhead
One-time bulk operations	Disabled	No impact

Performance Tips

1. Use batch writes - 10-100x faster than per-row for bulk operations
2. Enable streaming - Essential for large result sets
3. Tune batch size - 1,000-5,000 provides good balance between throughput and latency
4. Adjust fetch size - 1,000-5,000 rows works well for most workloads
5. Use connection pooling - Leverage dependency injection for efficient connection management

Security

• Identifier validation - Enabled by default to prevent SQL injection
• Parameterized queries - All queries use parameterized statements
• SSL/TLS support - Encrypt connections to database

Documentation

For comprehensive documentation including advanced scenarios, configuration reference, and best practices, see the PostgreSQL Connector documentation.

License

MIT License - see LICENSE file for details.