Table of Contents

Resiliency (retry & failover)

Inquiry's connection factories support two layers of open-time resiliency. Statement and transaction retry are deliberately out of scope — replays of partially applied work belong to the application, not the ORM.

Provider capability matrix

Not every provider exposes both layers. The table below shows what each provider supports:

Capability SQL Server PostgreSQL MySQL / MariaDB Oracle
Transient-fault retry Yes (AzureSql) Yes (CockroachDb, AuroraPostgreSql) No No
MaxAttempts / RetryBaseDelay / RetryMaxDelay Yes Yes — —
Backup-server failover (FailoverConnectionString) Yes Yes Yes Yes

MySQL and Oracle support failover only — they have no built-in transient-fault retry at the Inquiry level. If you need open-time retry on those engines, implement it in the application or use a driver-level mechanism (e.g. MySqlConnector Server=primary,backup, Oracle TNS ADDRESS_LIST/FAILOVER=on).

Transient-fault retry (cloud compatibility)

For cloud engines where throttling/failover faults are expected at connection open, the SQL Server and PostgreSQL providers retry the open with exponential backoff plus jitter, classifying faults with an engine-specific transient-error detector:

services.AddInquirySqlServer(connectionString, o =>
{
    o.Compatibility = SqlServerCompatibility.AzureSql; // enables open-time retry
    o.MaxAttempts = 5;                                 // default
    o.RetryBaseDelay = TimeSpan.FromMilliseconds(200); // default
    o.RetryMaxDelay = TimeSpan.FromSeconds(30);        // default
});

PostgreSQL exposes the same knobs via PostgreSqlCompatibility (CockroachDb, AuroraPostgreSql).

MySQL and Oracle do not expose retry options — see the capability matrix above.

Backup-server failover

Every server-based provider (SQL Server, PostgreSQL, MySQL/MariaDB, Oracle) accepts an optional failover connection string. When the primary fails to open — after any configured retry — the factory opens against the backup server instead:

services.AddInquiryPostgreSql(primaryConnectionString, o =>
{
    o.FailoverConnectionString = backupConnectionString;
});

Semantics:

  • Failover applies per open: every open tries the primary first, so traffic returns to the primary automatically once it recovers.
  • On providers with retry enabled, the retry policy applies to each server in turn. On providers without retry (MySQL, Oracle), each server gets a single open attempt.
  • Cancellation is never treated as a server fault — it propagates immediately.
  • If both servers fail, an AggregateException carrying both faults is thrown.

The backup server must be able to serve the workload (e.g. a read replica promoted for reads, a standby with replication). Inquiry does not replicate data or verify the failover target's role.

Driver-level alternatives remain available when preferred: SQL Server Failover Partner=, Npgsql multi-host connection strings (Host=a,b + Target Session Attributes), MySqlConnector Server=primary,backup, and Oracle TNS ADDRESS_LIST/FAILOVER=on. SQLite is an embedded file database, so server failover does not apply.

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