PeerDB uses Gopher Lua for scripting

See examples for sample scripts

Scripts can be added & edited in UI:

PeerDB Streams supports an onRecord function for complete control of message content. 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

For qrep mirrors transformRow can be defined. Row fields can be set to transform row. Schema may not be modified

For cdc mirrors transformRow will be called on the record’s rows by default, unless tranformRecord is defined. The latter can be useful for comparing old & new field values

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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