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changefeedccl: Projections and Filters in CDC.
Add a variant of CHANGEFEED statement that allows specification
of predicates and projections.
```
CREATE CHANGEFEED [INTO 'sink'] [WITH opt=val, ...]
AS SELECT .... FROM t WHERE ...
```
This changefeed variant can target at most 1 table (and 1 column
family) at a time. The expressions used as the projections and
filters can be almost any supported expression with some restrictions:
* Volatile functions not allowed.
* Subselects not allowed.
* Aggregate and window functions (i.e. functions operating over many
rows) not allowed.
* Some stable functions, notably functions which return MVCC
timestamp, are overridden to return MVCC timestamp of the event.
In addition, some CDC specific functions are provided:
* cdc_is_delete: returns true if the event is a deletion event.
* cdc_prev: returns JSON representation of the previous row state.
* cdc_updated_timestamp: returns event update timestamp (usually MVCC
timestamp, but can be different if e.g. undergoing schema changes)
Additional CDC specific functions will be added in the follow on PRs.
Few examples:
* Emit all but the deletion events:
```
CREATE CHANGEFEED INTO 'kafka://'
AS SELECT * FROM table
WHERE NOT cdc_is_delete()
```
* Emit all events that modified `important_col` column:
```
CREATE CHANGEFEED INTO 'kafka://' WITH diff
AS SELECT *, cdc_prev() AS previous
FROM important_table
WHERE important_col != cdc_prev()->'important_col'
```
* Emit few colums, as well as computed expresions:
```
CREATE CHANGEFEED INTO 'kafka://' WITH diff
AS SELECT warehouseID, (totalItems - orderedItems) as itemsAvailable
FROM warehouse
WHERE region='US/east';
```
When filter expression is specified, changefeed will now consult
optimizer so that the set of spans scanned by changefeed can be
restricted based on the predicate.
For example, given the following table and a changefeed:
```
CREATE TABLE warehouse (
region STRING,
warehouseID int,
....
PRIMARY KEY (region, warehouseID)
);
CREATE CHANGEFEED INTO 'kafka://' WITH diff
AS SELECT *
FROM warehouse
WHERE region='US/east';
```
The create changefeed will only scan table spans that contain `US/east`
region (and ignore all other table spans).
Release Notes (enterprise):
CHANGEFEED statement now supports general expressions: predicates and projections.
Projections allow customers to emit only the data that they care about,
including computed columns, while predicates (i.e. filters) allow them
to restrict the data that's emitted only to those events that match the
filter.
```
CREATE CHANGEFEED INTO 'kafka://' AS SELECT * FROM t WHERE NOT cdc_is_delete()
```- Loading branch information
Yevgeniy Miretskiy
committed
Jun 26, 2022
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,108 @@ | ||
| // Copyright 2022 The Cockroach Authors. | ||
| // | ||
| // Licensed as a CockroachDB Enterprise file under the Cockroach Community | ||
| // License (the "License"); you may not use this file except in compliance with | ||
| // the License. You may obtain a copy of the License at | ||
| // | ||
| // https://github.com/cockroachdb/cockroach/blob/master/licenses/CCL.txt | ||
|
|
||
| package cdceval | ||
|
|
||
| import ( | ||
| "context" | ||
|
|
||
| "github.com/cockroachdb/cockroach/pkg/ccl/changefeedccl/cdcevent" | ||
| "github.com/cockroachdb/cockroach/pkg/jobs/jobspb" | ||
| "github.com/cockroachdb/cockroach/pkg/keys" | ||
| "github.com/cockroachdb/cockroach/pkg/roachpb" | ||
| "github.com/cockroachdb/cockroach/pkg/sql" | ||
| "github.com/cockroachdb/cockroach/pkg/sql/catalog" | ||
| "github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode" | ||
| "github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror" | ||
| "github.com/cockroachdb/cockroach/pkg/sql/sem/eval" | ||
| "github.com/cockroachdb/cockroach/pkg/sql/sem/tree" | ||
| "github.com/cockroachdb/cockroach/pkg/util/hlc" | ||
| "github.com/cockroachdb/errors" | ||
| ) | ||
|
|
||
| // ConstrainPrimaryIndexSpanByFilter attempts to constrain table primary | ||
| // index span if changefeed expression (select clause) is specified. | ||
| // Returns possibly constrained spans, and a possibly modified (optimized) | ||
| // select clause. | ||
| func ConstrainPrimaryIndexSpanByFilter( | ||
| ctx context.Context, | ||
| execCtx sql.JobExecContext, | ||
| selectClause string, | ||
| descr catalog.TableDescriptor, | ||
| target jobspb.ChangefeedTargetSpecification, | ||
| includeVirtual bool, | ||
| ) (_ []roachpb.Span, updatedSelect string, _ error) { | ||
| if selectClause == "" { | ||
| return nil, "", errors.AssertionFailedf("unexpected empty filter") | ||
| } | ||
| sc, err := ParseChangefeedExpression(selectClause) | ||
| if err != nil { | ||
| return nil, "", pgerror.Wrap(err, pgcode.InvalidParameterValue, | ||
| "could not parse changefeed expression") | ||
| } | ||
|
|
||
| ed, err := newEventDescriptorForTarget(descr, target, schemaTS(execCtx), includeVirtual) | ||
| if err != nil { | ||
| return nil, "", err | ||
| } | ||
|
|
||
| evalCtx := &execCtx.ExtendedEvalContext().Context | ||
| spans, remainingFilter, err := constrainSpansBySelectClause( | ||
| ctx, execCtx, evalCtx, execCtx.ExecCfg().Codec, sc, ed) | ||
| if err != nil { | ||
| return nil, "", err | ||
| } | ||
|
|
||
| if remainingFilter != nil { | ||
| // non-nil remainingFilter implies we had sc.Where clause. | ||
| if remainingFilter == tree.DBoolTrue { | ||
| sc.Where = nil | ||
| } else { | ||
| sc.Where.Expr = remainingFilter | ||
| } | ||
| } | ||
|
|
||
| return spans, AsStringUnredacted(sc), nil | ||
| } | ||
|
|
||
| // constrainSpansBySelectClause is a helper that attempts to constrain primary | ||
| // index spans by the filter in the select clause. Returns constrained spans, | ||
| // along with the remaining filter. | ||
| func constrainSpansBySelectClause( | ||
| ctx context.Context, | ||
| sc sql.SpanConstrainer, | ||
| evalCtx *eval.Context, | ||
| codec keys.SQLCodec, | ||
| selectClause *tree.SelectClause, | ||
| ed *cdcevent.EventDescriptor, | ||
| ) ([]roachpb.Span, tree.Expr, error) { | ||
| // Predicate changefeed currently works on a single table only. | ||
| // Verify this assumption. | ||
| if len(selectClause.From.Tables) != 1 { | ||
| return nil, nil, errors.AssertionFailedf( | ||
| "expected 1 table expression, found %d", len(selectClause.From.Tables)) | ||
| } | ||
|
|
||
| if selectClause.Where == nil { | ||
| // Nothing to constrain. | ||
| return []roachpb.Span{ed.TableDescriptor().PrimaryIndexSpan(codec)}, nil, nil | ||
| } | ||
|
|
||
| tableName := tableNameOrAlias(ed.TableName, selectClause.From.Tables[0]) | ||
| semaCtx := newSemaCtx(ed) | ||
| return sc.ConstrainPrimaryIndexSpanByExpr( | ||
| ctx, sql.BestEffortConstrain, tableName, ed.TableDescriptor(), | ||
| evalCtx, semaCtx, selectClause.Where.Expr) | ||
| } | ||
|
|
||
| func schemaTS(execCtx sql.JobExecContext) hlc.Timestamp { | ||
| if execCtx.Txn() != nil { | ||
| return execCtx.Txn().ReadTimestamp() | ||
| } | ||
| return execCtx.ExecCfg().Clock.Now() | ||
| } |
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