Logging

A Logger interface is injected into the handler context with ctx.log. It is bound to the namespace sqd:processor:mapping. The context logger is a recommended way of logging for squid processors.

The Logger exposes different the following levels of severity, in the increasing order:

• TRACE
• DEBUG
• INFO
• WARN
• ERROR
• FATAL

By default, the logging level is set to INFO.

And here is an example:

processor.addEventHandler("Balances.Transfer", processTransfers);

async function processTransfers(
  ctx: EventHandlerContext<Store, { event: { args: true } }>
) {
  ctx.log.trace("Trace Log example");
  ctx.log.debug("Debug Log example");
  ctx.log.info("Info Log example");
  ctx.log.warn("Warn Log example");
  ctx.log.error("Error Log example");
  ctx.log.fatal("Fatal Log example");
}

Overriding the log level

The log level can be overridden by setting a matching namespace selector to one of the SQD_TRACE, ..., SQD_FATAL env variables. In particular, to set the handler logs level to DEBUG set the environment variable SQD_DEBUG to sqd:processor:mapping:

SQD_DEBUG=sqd:processor:mapping

The namespace selector supports wildcards, so one can also enable internal debug logs of @subsquid/substrate-processor with

SQD_DEBUG=sqd:processor:*

since all processor context loggers inherit the processor-level namespace sqd:processor.

Accessing logs of a deployed Squid

The processor logs can be inspected once the squid is deployed to Aquarium:

npx sqd squid logs <name>@<version> -f --level <level>

See CLI Reference for a full list of log options supported by Aquarium.