PeerDB uses Lua scripting for packaging messages for queues. In particular, Gopher Lua

Supported queues:

1. Kafka
2. PubSub
3. EventHubs

See examples for sample scripts

The script should define an onRecord function. Result may be a table instead of a string to specify partition key, metadata, etc. See queue specific pages for supported fields

If multiple return values are given, multiple records will be written

Scripts can be added & edited in UI:

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peerdb functions

The set of functions in global peerdb table are:

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RowColumns(row) table

Returns array of row’s column names

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RowColumnKind(row, column) string

Returns underlying Kind of row column, see qvalue/kind.go for list of kinds

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Now() [Time]

Returns current time as [Time]

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UUID(string?) [UUID]

Returns random [UUID], or parses passed in string

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Decimal(string | number)

Returns Decimal based on passed in value

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type(any) string

Returns fmt.Sprintf("%T", value) on underlying value of UserData. Returns nil for other types

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tostring(any) string

Returns fmt.Sprint(value) on underlying value of UserData. Returns nil for other types

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types

PeerDB exposes records as UserData:

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Record

Represents a CDC change

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kind

One of insert, update, delete, or relation. You will likely want to ignore relation messages

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row

Canonical row values of change. For update this is the new row. Keep in mind that Postgres does not send unchanged toast column values in CDC updates

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old

Previous row values, nil for insert

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new

New row values, nil for delete

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checkpoint

LSN of CDC message

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commit_time

CommitTime of record’s preceding BeginMessage

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target

Destination table of record defined by mirror

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source

Source table of record

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unchanged_columns

Update records have a table mapping unchanged toast columns to true

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Row

PeerDB row values which cannot be represented as Lua numbers or strings are wrapped in UserData. All of these types implement __tostring. Available types:

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I64 / U64

Represents signed/unsigned 64 bit integers. Implements comparisons with each other & __tostring support. There are 3 conversion properties:

• i64 cast to [I64]
• u64 cast to [U64]
• float64 cast to lua number
• hi returns highest 32 bits as an unsigned number
• lo returns lowest 32 bits as an unsigned number

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Time

Has properties for durations since Unix epoch. These are [I64] results, except unix which is a lua number

• unix_nano
• unix_micro
• unix_milli
• unix_second
• unix

& properties for datetime components as numbers:

• year
• month
• day
• yearday
• hour
• minute
• second
• nanosecond

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UUID

Index with [0..16) to access bytes (first element at index 0)

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BigInt

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sign

1, 0, or -1 depending on sign of value

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bytes

string of *big.Int Bytes method

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int64

value as [I64]

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is64

whether value can be represented by int64

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Decimal

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coefficient

[BigInt] representing digits

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coefficient64

[I64] representing digits

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exponent

Exponent, value of decimal is coefficient * (10 ^ exponent)

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bigint

Value of decimal as a BigInt

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int64

Value of decimal as a [I64]

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float

Value of decimal as a number

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package.preload

PeerDB offers some preloaded libraries, accessible via require:

library	description
bit32	bit32 API included in Lua 5.2
flatbuffers	flatbuffers API with 64-bit integer support, compatible with Lua generated using our patched flatc
json	JSON encoding/decoding
msgpack	msgpack encoding
utf8	utf8 API included in Lua 5.3