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Apache Griffin DSL Guide

Griffin DSL is designed for DQ measurement, as a SQL-like language, which describes the DQ domain request.

Apache Griffin DSL Syntax Description

Griffin DSL syntax is easy to learn as it's SQL-like, case insensitive.

Supporting process

  • logical operation: not, and, or, in, between, like, rlike, is null, is nan, =, !=, <>, <=, >=, <, >
  • mathematical operation: +, -, *, /, %
  • sql statement: as, where, group by, having, order by, limit

Keywords

  • null, nan, true, false
  • not, and, or
  • in, between, like, rlike, is
  • select, distinct, from, as, where, group, by, having, order, desc, asc, limit

Operators

  • !, &&, ||, =, !=, <, >, <=, >=, <>
  • +, -, *, /, %
  • (, )
  • ., [, ]

Literals

  • string: any string surrounded with a pair of " or ', with escape character \ if any request.
    e.g. "test", 'string 1', "hello \" world \" "
  • number: double or integer number.
    e.g. 123, 33.5
  • time: an integer with unit in a string, will be translated to an integer number by millisecond.
    e.g. 3d, 5h, 4ms
  • boolean: boolean value directly.
    e.g. true, false

Selections

  • selection head: data source name.
    e.g. source, target, `my table name`
  • all field selection: * or with data source name ahead.
    e.g. *, source.*, target.*
  • field selection: field name or with data source name ahead.
    e.g. source.age, target.name, user_id
  • index selection: integer between square brackets "[]" with field name ahead.
    e.g. source.attributes[3]
  • function selection: function name with brackets "()", with field name ahead or not.
    e.g. count(*), *.count(), source.user_id.count(), max(source.age)
  • alias: declare an alias after a selection.
    e.g. source.user_id as id, target.user_name as name

Math expressions

  • math factor: literal or function or selection or math exression with brackets.
    e.g. 123, max(1, 2, 3, 4), source.age, (source.age + 13)
  • unary math expression: unary math operator with factor.
    e.g. -(100 - source.score)
  • binary math expression: math factors with binary math operators.
    e.g. source.age + 13, score * 2 + ratio

Logical expression

  • in: in clause like sql.
    e.g. source.country in ("USA", "CHN", "RSA")
  • between: between clause like sql.
    e.g. source.age between 3 and 30, source.age between (3, 30)
  • like: like clause like sql.
    e.g. source.name like "%abc%"
  • rlike: rlike clause like spark sql.
    e.g. source.name rlike "^abc.*$"
  • is null: is null operator like sql.
    e.g. source.desc is not null
  • is nan: check if the value is not a number, the syntax like is null
    e.g. source.age is not nan
  • logical factor: math expression or logical expressions above or other logical expressions with brackets.
    e.g. (source.user_id = target.user_id AND source.age > target.age)
  • unary logical expression: unary logical operator with factor.
    e.g. NOT source.has_data, !(source.age = target.age)
  • binary logical expression: logical factors with binary logical operators, including and, or and comparison operators.
    e.g. source.age = target.age OR source.ticket = target.tck

Expression

  • expression: logical expression and math expression.

Function

  • argument: expression.
  • function: function name with arguments between brackets.
    e.g. max(source.age, target.age), count(*)

Clause

  • select clause: the result columns like sql select clause, we can ignore the word "select" in Apache Griffin DSL.
    e.g. select user_id.count(), age.max() as max, source.user_id.count() as cnt, source.age.min()
  • from clause: the table name like sql from clause, in which the data source name must be one of data source names or the output table name of the former rule steps, we can ignore this clause by configoring the data source name.
    e.g. from source, from `target`
  • where clause: the filter condition like sql where clause, optional.
    e.g. where source.id = target.id and source.age = target.age
  • group-by clause: like the group-by clause in sql, optional. Optional having clause could be following.
    e.g. group by cntry, group by gender having count(*) > 50
  • order-by clause: like the order-by clause, optional.
    e.g. order by name, order by first_name desc, age asc
  • limit clause: like the limit clause in sql, optional.
    e.g. limit 5

Accuracy Rule

Accuracy rule expression in Apache Griffin DSL is a logical expression, telling the mapping relation between data sources.
e.g. source.id = target.id and source.name = target.name and source.age between (target.age, target.age + 5)

Profiling Rule

Profiling rule expression in Apache Griffin DSL is a sql-like expression, with select clause ahead, following optional from clause, where clause, group-by clause, order-by clause, limit clause in order.
e.g. source.gender, source.id.count() where source.age > 20 group by source.gender, select country, max(age), min(age), count(*) as cnt from source group by country order by cnt desc limit 5

Distinctness Rule

Distinctness rule expression in Apache Griffin DSL is a list of selection expressions separated by comma, indicates the columns to check if is distinct. e.g. name, age, name, (age + 1) as next_age

Timeliness Rule

Timeliness rule expression in Apache Griffin DSL is a list of selection expressions separated by comma, indicates the input time and output time (calculate time as default if not set).
e.g. ts, ts, end_ts

Apache Griffin DSL translation to SQL

Apache Griffin DSL is defined for DQ measurement, to describe DQ domain problem.
Actually, in Apache Griffin, we get Apache Griffin DSL rules, translate them into spark-sql rules for calculation in spark-sql engine.
In DQ domain, there're multiple dimensions, we need to translate them in different ways.

Accuracy

For accuracy, we need to get the match count between source and target, the rule describes the mapping relation between data sources. Apache Griffin needs to translate the dsl rule into multiple sql rules.
For example, the dsl rule is source.id = target.id and source.name = target.name, which represents the match condition of accuracy. After the translation, the sql rules are as below:

  • get miss items from source: SELECT source.* FROM source LEFT JOIN target ON coalesce(source.id, '') = coalesce(target.id, '') and coalesce(source.name, '') = coalesce(target.name, '') WHERE (NOT (source.id IS NULL AND source.name IS NULL)) AND (target.id IS NULL AND target.name IS NULL), save as table miss_items.
  • get miss count: SELECT COUNT(*) AS miss FROM miss_items, save as table miss_count.
  • get total count from source: SELECT COUNT(*) AS total FROM source, save as table total_count.
  • get accuracy metric: SELECT miss_count.miss AS miss, total_count.total AS total, (total_count.total - miss_count.miss) AS matched FROM miss_count FULL JOIN total_count, save as table accuracy.

After the translation, the metrics will be persisted in table accuracy.

Profiling

For profiling, the request is always the aggregation function of data, the rule is mainly the same as sql, but only supporting select, from, where, group-by, having, order-by, limit clauses, which can describe most of the profiling requests. If any complicate request, you can use sql rule directly to describe it.
For example, the dsl rule is source.cntry, source.id.count(), source.age.max() group by source.cntry, which represents the profiling requests. After the translation, the sql rule is as below:

  • profiling sql rule: SELECT source.cntry, count(source.id), max(source.age) FROM source GROUP BY source.cntry, save as table profiling.

After the translation, the metrics will be persisted in table profiling.

Distinctness

For distinctness, is to find out the duplicate items of data, the same as uniqueness in batch mode, but with some differences in streaming mode. In most time, you need distinctness other than uniqueness. For example, the dsl rule is name, age, which represents the distinct requests, in this case, source and target are the same data set. After the translation, the sql rule is as below:

  • total count of source: SELECT COUNT(*) AS total FROM source, save as table total_count.
  • group by fields: SELECT name, age, (COUNT(*) - 1) AS dup, TRUE AS dist FROM source GROUP BY name, age, save as table dup_count.
  • distinct metric: SELECT COUNT(*) AS dist_count FROM dup_count WHERE dist, save as table distinct_metric.
  • source join distinct metric: SELECT source.*, dup_count.dup AS dup, dup_count.dist AS dist FROM source LEFT JOIN dup_count ON source.name = dup_count.name AND source.age = dup_count.age, save as table dist_joined.
  • add row number: SELECT *, ROW_NUMBER() OVER (DISTRIBUTE BY name, age SORT BY dist) row_num FROM dist_joined, save as table row_numbered.
  • duplicate records: SELECT name, age, dup FROM row_numbered WHERE NOT dist OR row_num > 1, save as table dup_records.
  • duplicate metric: SELECT name, age, dup, COUNT(*) AS num FROM dup_records GROUP BY name, age, dup, save as table dup_metric.

After the translation, the metrics will be persisted in table distinct_metric and dup_metric.

Timeliness

For timeliness, is to measure the latency of each item, and get the statistics of the latencies.
For example, the dsl rule is ts, out_ts, the first column means the input time of item, the second column means the output time of item, if not set, __tmst will be the default output time column. After the translation, the sql rule is as below:

  • get input and output time column: SELECT *, ts AS _bts, out_ts AS _ets FROM source, save as table origin_time.
  • get latency: SELECT *, (_ets - _bts) AS latency FROM origin_time, save as table lat.
  • get timeliness metric: SELECT CAST(AVG(latency) AS BIGINT) AS avg, MAX(latency) AS max, MIN(latency) AS min FROM lat, save as table time_metric.

After the translation, the metrics will be persisted in table time_metric.

Alternative Rules

You can simply use Griffin DSL rule to describe your problem in DQ domain, for some complicate requirement, you can also use some alternative rules supported by Apache Griffin.

Spark sql

Griffin supports spark-sql directly, you can write rule in sql like this:

{
	"dsl.type": "spark-sql",
	"name": "source",
	"rule": "SELECT count(id) AS cnt, max(timestamp) AS fresh_time FROM source"
}

Griffin will calculate it in spark-sql engine directly.

Data frame operation

Griffin supports some other operations on data frame in spark, like converting json string data frame into extracted data frame with extracted object schema. For example:

{
	"dsl.type": "df-opr",
	"name": "ext_source",
	"rule": "from_json",
	"details": {
		"df.name": "json_source"
	}
}

Griffin will do the operation to extract json strings.
Actually, you can also extend the df-opr engine and df-opr adaptor in Apache Griffin to support more types of data frame operations.

Tips

Griffin engine runs on spark, it might work in two phases, pre-proc phase and run phase.

  • Pre-proc phase: Apache Griffin calculates data source directly, to get appropriate data format, as a preparation for DQ calculation. In this phase, you can use df-opr and spark-sql rules.
    After preparation, to support streaming DQ calculation, a timestamp column will be added in each row of data, so the data frame in run phase contains an extra column named "__tmst".
  • Run phase: Apache Griffin calculates with prepared data, to get the DQ metrics. In this phase, you can use griffin-dsl, spark-sql rules, and a part of df-opr rules.
    For griffin-dsl rule, Apache Griffin translates it into spark-sql rule with a group-by condition for column "__tmst", it's useful for especially streaming DQ calculation.
    But for spark-sql rule, Apache Griffin use it directly, you need to add the "__tmst" column in your spark-sql rule explicitly, or you can't get correct metrics result after calculation.