Module cdc 

Change Data Capture (CDC) Stream support.

Emits mutations to a Redis Stream for external replication agents. The stream key is {redis_prefix}__local__:cdc where __local__ indicates node-local infrastructure that should not be replicated itself.

Stream Format

PUT operation

XADD {prefix}__local__:cdc MAXLEN ~ 100000 *
  op    "PUT"
  key   "uk.nhs.patient.12345"
  hash  "a1b2c3..."                # content_hash for dedup
  data  <zstd(content)>            # compressed payload
  meta  '{"content_type":"json","version":3,"updated_at":1735776000000}'

DELETE operation

XADD {prefix}__local__:cdc MAXLEN ~ 100000 *
  op    "DEL"
  key   "uk.nhs.patient.12345"

Compression Strategy

Data is zstd-compressed before writing to the stream, unless it already has zstd magic bytes (to avoid double-compression).

Structs

CdcEntry

A CDC entry ready to be written to the stream

CdcMeta

Metadata for CDC PUT entries

Enums

CdcFieldValue

Field value types for CDC entries

CdcOp

CDC operation type

Constants

CDC_STREAM_SUFFIX

CDC stream suffix (appended to redis_prefix)

Functions

cdc_stream_key

Build the full CDC stream key from an optional prefix

is_zstd_compressed

Check if data appears to be zstd-compressed

maybe_compress

Compress data with zstd, unless it’s already zstd-compressed.

maybe_decompress

Decompress zstd data if it has the magic header, otherwise return as-is.