influxdata/influxdb · error · WriteError::Fail

Cannot write

Error message

Cannot write: {0}

What it means

WriteError::Fail is the generic variant of the write error enum used by WriteEndpoint implementations in the Python plugin API; it wraps any underlying write failure as 'Cannot write: {cause}'. It indicates the requested line protocol write could not be performed, with the concrete cause boxed inside the error.

Solutions

1. Read the inner cause after 'Cannot write: ' to identify the actual failure and fix that first
2. Validate line protocol syntax and field types against the target table schema before writing
3. Confirm the target database exists (create it if needed) and that credentials/permissions allow writes
4. Check network connectivity and endpoint configuration if the write goes over HTTP

def validate_lp(lines, expected_types):
    for line in lines:
        if not line or ' ' not in line:
            raise ValueError(f'invalid line protocol: {line!r}')

try:
    api.write_to_database('mydb', line_protocol)
except Exception as e:
    # inspect str(e); 'Cannot write: ...' wraps the underlying cause
    logger.error(f'write failed: {e}')
    raise

When it happens

Trigger: Any write_lp call on a WriteEndpoint whose underlying storage/HTTP write fails, with the inner error (network failure, invalid line protocol, auth failure, database not found) preserved in the message.

Common situations: Plugin writes line protocol with schema/type conflicts against an existing table; write target database does not exist; network or auth failure when writing via HTTP to an InfluxDB endpoint; malformed line protocol rejected by the server.

Related errors

• internal writes are not supported by the write accumulator
• line protocol parse failed
• cannot write to soft-deleted database
• column ' ' ( ) is not defined in table ' ' of database ' '…
• column type mismatch for column

AI-assisted analysis of influxdata/influxdb@06200ef96b (2026-09-19). Data as JSON: /api/errors/69f6b3fecfa18664. Report an issue: GitHub.

Appendix: source

Thrown at influxdb3_py_api/src/write.rs:54

        _ingest_time: Time,
        _no_sync: bool,
    ) -> Result<(), WriteError> {
        match target {
            WriteTarget::User(database) if database.as_str() == INTERNAL_DB_NAME => {
                Err(WriteError::InternalWriteUnsupported)
            }
            WriteTarget::User(database) => {
                self.push(database.as_str().to_owned(), lp.to_owned());
                Ok(())
            }
            WriteTarget::Internal => Err(WriteError::InternalWriteUnsupported),
        }
    }
}

#[derive(Debug, Error)]
pub enum WriteError {
    #[error("Cannot write: {0}")]
    Fail(Box<dyn std::error::Error + Send + Sync>),

    #[error("internal writes are not supported by the write accumulator")]
    InternalWriteUnsupported,
}

#[derive(Debug, Clone)]
pub enum WriteTarget {
    /// Write into a user database.
    User(DatabaseName),
    /// Write into the one system-managed internal database.
    Internal,
}

#[async_trait]
pub trait WriteEndpoint: std::fmt::Debug + Send + Sync + 'static {
    async fn write_lp(
        &self,

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