Field Glossary
Most log lines carry structured fields alongside their human-readable message. Because message wording can change between Service versions, filter on these fields rather than the message text. The table below covers the fields on most lines, but a line can carry many more (especially with metadata expanded), and each source connector adds its own. Treat fields not listed here as additional context, and see the Detailed Event Reference for fields specific to individual events.Severity and Recovery
A line’s severity (level) does not necessarily tell you whether you need to act. Most error and warn lines describe transient events that the Service recovers from on its own:
- Per-session errors stay isolated to the affected client.
Sync stream errorandStreaming sync request failedtear down a single stream, and that client reconnects on its own. Service-wide failures such as a pod restart are the exception. They interrupt all connected clients until the Service recovers. - The replicator retries source-database operations automatically, so transient connection drops, query timeouts, and keep-alive failures are caught, logged, and retried.
- Some
errorlines, such asReplication failed., trigger a pod restart that the supervisor handles automatically. Operator action is needed only when the cause persists across restarts.
MongoDB is the storage backend for all PowerSync Cloud instances, which some lines reflect (for example
Successfully activated storage: mongodb. or checksum errors like PSYNC_S2403). If you self-host on Postgres-backed storage, those lines look different.Sync & API Logs
Produced by the PowerSync Service API pods. These cover client sync sessions (WebSocket and HTTP), HTTP API requests, checkpoint calculations, and write checkpoint endpoints.Sync Session Lifecycle
These events trace a client’s sync session from start to finish. Searching for arid returns both ends.
A short
stream_ms paired with operations_synced: 0 usually means the connection was opened and torn down before any sync line was sent. This is normal when many clients reconnect at once, or when a client cancels quickly.
For the full field breakdown of each line, see Sync session field details below.
Close Reasons
Theclose_reason field on Sync stream complete takes one of these values:
Checkpoint Events
The PowerSync Service computes checkpoints to decide whether each connected client needs new data. In steady state you mostly seeUpdated checkpoint lines with empty updated/removed arrays, which are rechecks where nothing changed for that user.
Common Errors in Sync & API Logs
For the full code list, see Error Codes Reference.
Replicator Logs
Produced by the replication pod that pulls changes from your source database (Postgres, MongoDB, MySQL, or MSSQL) and writes them into the PowerSync storage layer.Most replicator lines are prefixed with the Sync Config identifier in brackets, for example
[powersync_69b93ff7358aa0646ff0dbca_1_e6dc]. The format is [powersync_<instance_id>_<group_id>_<hash>]. The group_id increments when the Sync Config changes, so a new version means a new group. Use this prefix to scope log queries to a particular Sync Config iteration.Streaming Replication (Steady State)
Once initial replication is done, the replicator streams changes. TheFlushed line is the most important steady-state line and the bulk of normal replicator logs.
The same numbers appear as a structured
flushed object on the line, easier to filter on than the message text:
Replication lag is absent, the flush had no source-side change timestamps to derive it from. This happens only on snapshot flushes, never steady-state.
Replication Health
These lines report problems in the replication loop. Almost all are non-fatal, and the replicator handles them on its own.Common Errors in Replicator Logs
For the full code list and additional connector-specific codes, see Error Codes Reference.
Detailed Event Reference
The sections above cover the most common lines. The events below are lower-frequency or verbose, collapsed here to keep the page scannable but documented in full.Sync & API Logs
Sync session field details
Sync session field details
Checkpoint payload anatomy
Checkpoint payload anatomy
Example payloads:
Structured fields on the same line include
checkpoint (the op_id), buckets (count), parameter_query_results (count), and on Updated checkpoint only, updated and removed counts as integers. These are easier to filter on than parsing the message body.HTTP endpoint and write checkpoint events
HTTP endpoint and write checkpoint events
Every HTTP access log line carries these structured fields. They are not visible in the rendered message but are filterable.
Concurrency and queueing
Concurrency and queueing
These appear when the API pod is near its configured concurrent-sync limit.
Frequent
Sync concurrency limit reached typically means traffic exceeds what the pod can handle, or the per-pod cap is set too low. See Production Readiness Guide.Replication propagation (observed from the API pod)
Replication propagation (observed from the API pod)
A long delay between these two lines means the replicator is behind. If sustained, see Replication Lag.
Replicator Logs
Startup and lifecycle
Startup and lifecycle
Fired when a replication pod starts, stops, or restarts. Outside of a deploy, these usually mean the pod was killed and restarted by the supervisor.
Sync Config changes
Sync Config changes
Shutdown sequence
Shutdown sequence
Triggered by SIGTERM (deploys, scale-down) or by a fatal error. A clean shutdown ends with If you see
Exiting. Lines you will see in order:Replication failed. or Fatal replication error before the shutdown lines, the pod is being restarted by the supervisor after a crash.Initial Replication
Initial Replication
The first time a Sync Config iteration is set up, every table covered by it is copied over. The exact wording differs by source database.
Snapshot completion and replication slot management
Snapshot completion and replication slot management
Streaming replication variants
Streaming replication variants
Beyond the
Flushed line, the streaming phase emits these connector-specific lines.The
Flushed line’s structured flushed object maps to the message components as follows:Schema changes
Schema changes
CDC polling (MSSQL only)
CDC polling (MSSQL only)
The MSSQL connector polls CDC capture tables rather than streaming a logical replication slot.