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A universal transaction manager that achieves database-agnostic transactions and distributed transactions that span multiple databases
package com.scalar.db.storage.dynamo;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.primitives.UnsignedBytes;
import com.scalar.db.api.Consistency;
import com.scalar.db.api.Get;
import com.scalar.db.api.Scan;
import com.scalar.db.api.Scan.Ordering;
import com.scalar.db.api.Scan.Ordering.Order;
import com.scalar.db.api.ScanAll;
import com.scalar.db.api.Scanner;
import com.scalar.db.api.Selection;
import com.scalar.db.api.TableMetadata;
import com.scalar.db.common.EmptyScanner;
import com.scalar.db.common.TableMetadataManager;
import com.scalar.db.exception.storage.ExecutionException;
import com.scalar.db.io.Column;
import com.scalar.db.io.Key;
import com.scalar.db.storage.dynamo.bytes.BytesUtils;
import com.scalar.db.storage.dynamo.bytes.KeyBytesEncoder;
import com.scalar.db.util.ScalarDbUtils;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.ThreadSafe;
import software.amazon.awssdk.core.SdkBytes;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbRequest;
import software.amazon.awssdk.services.dynamodb.model.GetItemRequest;
import software.amazon.awssdk.services.dynamodb.model.QueryRequest;
import software.amazon.awssdk.services.dynamodb.model.ScanRequest;
/**
* A handler class for select statement
*
* @author Yuji Ito, Toshihiro Suzuki
*/
@ThreadSafe
public class SelectStatementHandler {
private final DynamoDbClient client;
private final TableMetadataManager metadataManager;
private final String namespacePrefix;
/**
* Constructs a {@code SelectStatementHandler} with the specified {@link DynamoDbClient} and a new
* {@link TableMetadataManager}
*
* @param client {@code DynamoDbClient}
* @param metadataManager {@code TableMetadataManager}
* @param namespacePrefix a namespace prefix
*/
@SuppressFBWarnings("EI_EXPOSE_REP2")
public SelectStatementHandler(
DynamoDbClient client,
TableMetadataManager metadataManager,
Optional namespacePrefix) {
this.client = checkNotNull(client);
this.metadataManager = checkNotNull(metadataManager);
this.namespacePrefix = namespacePrefix.orElse("");
}
@Nonnull
public Scanner handle(Selection selection) throws ExecutionException {
TableMetadata tableMetadata = metadataManager.getTableMetadata(selection);
if (selection instanceof Get) {
selection = copyAndAppendNamespacePrefix((Get) selection);
} else {
selection = copyAndAppendNamespacePrefix((Scan) selection);
}
try {
if (!(selection instanceof ScanAll)
&& ScalarDbUtils.isSecondaryIndexSpecified(selection, tableMetadata)) {
return executeScanWithIndex(selection, tableMetadata);
}
if (selection instanceof Get) {
return executeGet((Get) selection, tableMetadata);
} else if (selection instanceof ScanAll) {
return executeFullScan((ScanAll) selection, tableMetadata);
} else {
return executeScan((Scan) selection, tableMetadata);
}
} catch (DynamoDbException e) {
throw new ExecutionException(e.getMessage(), e);
}
}
private Scanner executeGet(Get get, TableMetadata tableMetadata) {
DynamoOperation dynamoOperation = new DynamoOperation(get, tableMetadata);
GetItemRequest.Builder builder =
GetItemRequest.builder()
.tableName(dynamoOperation.getTableName())
.key(dynamoOperation.getKeyMap());
if (!get.getProjections().isEmpty()) {
Map expressionAttributeNames = new HashMap<>();
projectionExpression(builder, get, expressionAttributeNames);
builder.expressionAttributeNames(expressionAttributeNames);
}
if (get.getConsistency() != Consistency.EVENTUAL) {
builder.consistentRead(true);
}
return new GetItemScanner(
client, builder.build(), new ResultInterpreter(get.getProjections(), tableMetadata));
}
private Scanner executeScanWithIndex(Selection selection, TableMetadata tableMetadata) {
DynamoOperation dynamoOperation = new DynamoOperation(selection, tableMetadata);
Column keyColumn = selection.getPartitionKey().getColumns().get(0);
String column = keyColumn.getName();
String indexTable = dynamoOperation.getGlobalIndexName(column);
QueryRequest.Builder builder =
QueryRequest.builder().tableName(dynamoOperation.getTableName()).indexName(indexTable);
String expressionColumnName = DynamoOperation.COLUMN_NAME_ALIAS + "0";
String condition = expressionColumnName + " = " + DynamoOperation.VALUE_ALIAS + "0";
ValueBinder binder = new ValueBinder(DynamoOperation.VALUE_ALIAS);
keyColumn.accept(binder);
Map bindMap = binder.build();
builder.keyConditionExpression(condition).expressionAttributeValues(bindMap);
Map expressionAttributeNames = new HashMap<>();
expressionAttributeNames.put(expressionColumnName, column);
if (!selection.getProjections().isEmpty()) {
projectionExpression(builder, selection, expressionAttributeNames);
}
builder.expressionAttributeNames(expressionAttributeNames);
if (selection instanceof Scan) {
Scan scan = (Scan) selection;
if (scan.getLimit() > 0) {
builder.limit(scan.getLimit());
}
}
com.scalar.db.storage.dynamo.request.QueryRequest request =
new com.scalar.db.storage.dynamo.request.QueryRequest(client, builder.build());
return new QueryScanner(
request, new ResultInterpreter(selection.getProjections(), tableMetadata));
}
private Scanner executeScan(Scan scan, TableMetadata tableMetadata) {
DynamoOperation dynamoOperation = new DynamoOperation(scan, tableMetadata);
QueryRequest.Builder builder = QueryRequest.builder().tableName(dynamoOperation.getTableName());
if (!setConditions(builder, scan, tableMetadata)) {
// if setConditions() fails, return an empty scanner
return new EmptyScanner();
}
if (!scan.getOrderings().isEmpty()) {
Ordering ordering = scan.getOrderings().get(0);
if (ordering.getOrder() != tableMetadata.getClusteringOrder(ordering.getColumnName())) {
// reverse scan
builder.scanIndexForward(false);
}
}
if (scan.getLimit() > 0) {
builder.limit(scan.getLimit());
}
if (!scan.getProjections().isEmpty()) {
Map expressionAttributeNames = new HashMap<>();
projectionExpression(builder, scan, expressionAttributeNames);
builder.expressionAttributeNames(expressionAttributeNames);
}
if (scan.getConsistency() != Consistency.EVENTUAL) {
builder.consistentRead(true);
}
com.scalar.db.storage.dynamo.request.QueryRequest queryRequest =
new com.scalar.db.storage.dynamo.request.QueryRequest(client, builder.build());
return new QueryScanner(
queryRequest, new ResultInterpreter(scan.getProjections(), tableMetadata));
}
private Scanner executeFullScan(ScanAll scan, TableMetadata tableMetadata) {
DynamoOperation dynamoOperation = new DynamoOperation(scan, tableMetadata);
ScanRequest.Builder builder = ScanRequest.builder().tableName(dynamoOperation.getTableName());
if (scan.getLimit() > 0) {
builder.limit(scan.getLimit());
}
if (!scan.getProjections().isEmpty()) {
Map expressionAttributeNames = new HashMap<>();
projectionExpression(builder, scan, expressionAttributeNames);
builder.expressionAttributeNames(expressionAttributeNames);
}
if (scan.getConsistency() != Consistency.EVENTUAL) {
builder.consistentRead(true);
}
com.scalar.db.storage.dynamo.request.ScanRequest requestWrapper =
new com.scalar.db.storage.dynamo.request.ScanRequest(client, builder.build());
return new QueryScanner(
requestWrapper, new ResultInterpreter(scan.getProjections(), tableMetadata));
}
private void projectionExpression(
DynamoDbRequest.Builder builder,
Selection selection,
Map expressionAttributeNames) {
assert builder instanceof GetItemRequest.Builder
|| builder instanceof QueryRequest.Builder
|| builder instanceof ScanRequest.Builder;
List projections = new ArrayList<>(selection.getProjections().size());
for (String projection : selection.getProjections()) {
String alias = DynamoOperation.COLUMN_NAME_ALIAS + expressionAttributeNames.size();
projections.add(alias);
expressionAttributeNames.put(alias, projection);
}
String projectionExpression = String.join(",", projections);
if (builder instanceof GetItemRequest.Builder) {
((GetItemRequest.Builder) builder).projectionExpression(projectionExpression);
} else if (builder instanceof QueryRequest.Builder) {
((QueryRequest.Builder) builder).projectionExpression(projectionExpression);
} else {
((ScanRequest.Builder) builder).projectionExpression(projectionExpression);
}
}
private boolean setConditions(
QueryRequest.Builder builder, Scan scan, TableMetadata tableMetadata) {
List conditions = new ArrayList<>();
Map bindMap = new HashMap<>();
setConditionForPartitionKey(scan, tableMetadata, conditions, bindMap);
// If the scan is for DESC clustering order, use the end clustering key as a start key and the
// start clustering key as an end key
boolean scanForDescClusteringOrder = isScanForDescClusteringOrder(scan, tableMetadata);
Optional startKey =
scanForDescClusteringOrder ? scan.getEndClusteringKey() : scan.getStartClusteringKey();
boolean startInclusive =
scanForDescClusteringOrder ? scan.getEndInclusive() : scan.getStartInclusive();
Optional endKey =
scanForDescClusteringOrder ? scan.getStartClusteringKey() : scan.getEndClusteringKey();
boolean endInclusive =
scanForDescClusteringOrder ? scan.getStartInclusive() : scan.getEndInclusive();
if (startKey.isPresent() && endKey.isPresent()) {
if (!setBetweenCondition(
startKey.get(),
startInclusive,
endKey.get(),
endInclusive,
tableMetadata,
conditions,
bindMap)) {
return false;
}
} else {
if (startKey.isPresent()) {
if (startKey.get().size() == 1) {
if (!setStartCondition(
startKey.get(), startInclusive, tableMetadata, conditions, bindMap)) {
return false;
}
} else {
// if a start key with multiple values specified and no end key specified, use between
// condition and use a key based on the start key without the last value as an end key
if (!setBetweenCondition(
startKey.get(),
startInclusive,
getKeyWithoutLastValue(startKey.get()),
true,
tableMetadata,
conditions,
bindMap)) {
return false;
}
}
}
if (endKey.isPresent()) {
if (endKey.get().size() == 1) {
setEndCondition(endKey.get(), endInclusive, tableMetadata, conditions, bindMap);
} else {
// if an end key with multiple values specified and no start key specified, use between
// condition and use a key based on the end key without the last value as a start key
if (!setBetweenCondition(
getKeyWithoutLastValue(endKey.get()),
true,
endKey.get(),
endInclusive,
tableMetadata,
conditions,
bindMap)) {
return false;
}
}
}
}
builder
.keyConditionExpression(String.join(" AND ", conditions))
.expressionAttributeValues(bindMap);
return true;
}
private Key getKeyWithoutLastValue(Key originalKey) {
Key.Builder keyBuilder = Key.newBuilder();
for (int i = 0; i < originalKey.get().size() - 1; i++) {
keyBuilder.add(originalKey.get().get(i));
}
return keyBuilder.build();
}
private void setConditionForPartitionKey(
Scan scan,
TableMetadata tableMetadata,
List conditions,
Map bindMap) {
conditions.add(DynamoOperation.PARTITION_KEY + " = " + DynamoOperation.PARTITION_KEY_ALIAS);
DynamoOperation dynamoOperation = new DynamoOperation(scan, tableMetadata);
ByteBuffer concatenatedPartitionKey = dynamoOperation.getConcatenatedPartitionKey();
bindMap.put(
DynamoOperation.PARTITION_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(concatenatedPartitionKey)).build());
}
private boolean setBetweenCondition(
Key startKey,
boolean startInclusive,
Key endKey,
boolean endInclusive,
TableMetadata tableMetadata,
List conditions,
Map bindMap) {
ByteBuffer startKeyBytes = getKeyBytes(startKey, tableMetadata);
if (!startInclusive) {
// if exclusive scan for the start key, we use the closest next bytes of the start key bytes
Optional closestNextBytes = BytesUtils.getClosestNextBytes(startKeyBytes);
if (!closestNextBytes.isPresent()) {
// if we can't find the closest next bytes of the start key bytes, return false. That means
// we should return empty results in this case
return false;
}
startKeyBytes = closestNextBytes.get();
}
ByteBuffer endKeyBytes = getKeyBytes(endKey, tableMetadata);
boolean fullClusteringKeySpecified =
endKey.size() == tableMetadata.getClusteringKeyNames().size();
if (fullClusteringKeySpecified) {
if (!endInclusive) {
// if full end key specified, and it's an exclusive scan for the end key, we use the closest
// previous bytes of the end key bytes for the between condition
Optional closestPreviousBytes = BytesUtils.getClosestPreviousBytes(endKeyBytes);
if (!closestPreviousBytes.isPresent()) {
// if we can't find the closest previous bytes of the end key bytes, return false. That
// means we should return empty results in this case
return false;
}
endKeyBytes = closestPreviousBytes.get();
}
} else {
if (endInclusive) {
// if partial end key specified, and it's an inclusive scan for the end key, we use the
// closest next bytes of the end key bytes for the between condition
Optional closestNextBytes = BytesUtils.getClosestNextBytes(endKeyBytes);
if (!closestNextBytes.isPresent()) {
// if we can't find the closest next bytes of the end key bytes, set start condition with
// the start key
return setStartCondition(startKey, startInclusive, tableMetadata, conditions, bindMap);
}
endKeyBytes = closestNextBytes.get();
}
}
byte[] start = BytesUtils.toBytes(startKeyBytes);
byte[] end = BytesUtils.toBytes(endKeyBytes);
if (UnsignedBytes.lexicographicalComparator().compare(start, end) > 0) {
// if the start key bytes are greater than the end key bytes, return false. That means we
// should return empty results in this case. This situation could happen when full clustering
// keys specified and scanning exclusively
return false;
}
conditions.add(
DynamoOperation.CLUSTERING_KEY
+ " BETWEEN "
+ DynamoOperation.START_CLUSTERING_KEY_ALIAS
+ " AND "
+ DynamoOperation.END_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.START_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteArray(start)).build());
bindMap.put(
DynamoOperation.END_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteArray(end)).build());
return true;
}
private boolean setStartCondition(
Key startKey,
boolean startInclusive,
TableMetadata tableMetadata,
List conditions,
Map bindMap) {
ByteBuffer startKeyBytes = getKeyBytes(startKey, tableMetadata);
boolean fullClusteringKeySpecified =
startKey.size() == tableMetadata.getClusteringKeyNames().size();
if (fullClusteringKeySpecified) {
conditions.add(
DynamoOperation.CLUSTERING_KEY
+ (startInclusive ? " >= " : " > ")
+ DynamoOperation.START_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.START_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(startKeyBytes)).build());
} else {
if (startInclusive) {
conditions.add(
DynamoOperation.CLUSTERING_KEY + " >= " + DynamoOperation.START_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.START_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(startKeyBytes)).build());
} else {
// if partial start key specified, and it's an exclusive scan for the start key, we use
// the closest next bytes of the start key bytes for the grater than or equal condition
Optional closestNextBytes = BytesUtils.getClosestNextBytes(startKeyBytes);
if (closestNextBytes.isPresent()) {
conditions.add(
DynamoOperation.CLUSTERING_KEY + " >= " + DynamoOperation.START_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.START_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(closestNextBytes.get())).build());
} else {
// if we can't find the closest next bytes of the start key bytes, return false. That
// means we should return empty results in this case
return false;
}
}
}
return true;
}
private void setEndCondition(
Key endKey,
boolean endInclusive,
TableMetadata tableMetadata,
List conditions,
Map bindMap) {
ByteBuffer endKeyBytes = getKeyBytes(endKey, tableMetadata);
boolean fullClusteringKeySpecified =
endKey.size() == tableMetadata.getClusteringKeyNames().size();
if (fullClusteringKeySpecified) {
conditions.add(
DynamoOperation.CLUSTERING_KEY
+ (endInclusive ? " <= " : " < ")
+ DynamoOperation.END_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.END_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(endKeyBytes)).build());
} else {
if (endInclusive) {
// if partial end key specified, and it's an inclusive scan for the end key, we use the
// closest next bytes of the end key bytes for the less than condition
BytesUtils.getClosestNextBytes(endKeyBytes)
.ifPresent(
k -> {
conditions.add(
DynamoOperation.CLUSTERING_KEY
+ " < "
+ DynamoOperation.END_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.END_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(k)).build());
});
} else {
conditions.add(
DynamoOperation.CLUSTERING_KEY + " < " + DynamoOperation.END_CLUSTERING_KEY_ALIAS);
bindMap.put(
DynamoOperation.END_CLUSTERING_KEY_ALIAS,
AttributeValue.builder().b(SdkBytes.fromByteBuffer(endKeyBytes)).build());
}
}
}
private ByteBuffer getKeyBytes(Key key, TableMetadata tableMetadata) {
return new KeyBytesEncoder().encode(key, tableMetadata.getClusteringOrders());
}
private boolean isScanForDescClusteringOrder(Scan scan, TableMetadata tableMetadata) {
if (scan.getStartClusteringKey().isPresent()) {
Key startClusteringKey = scan.getStartClusteringKey().get();
String lastValueName = startClusteringKey.get().get(startClusteringKey.size() - 1).getName();
return tableMetadata.getClusteringOrder(lastValueName) == Order.DESC;
}
if (scan.getEndClusteringKey().isPresent()) {
Key endClusteringKey = scan.getEndClusteringKey().get();
String lastValueName = endClusteringKey.get().get(endClusteringKey.size() - 1).getName();
return tableMetadata.getClusteringOrder(lastValueName) == Order.DESC;
}
return false;
}
private Get copyAndAppendNamespacePrefix(Get get) {
assert get.forNamespace().isPresent();
return Get.newBuilder(get).namespace(namespacePrefix + get.forNamespace().get()).build();
}
private Scan copyAndAppendNamespacePrefix(Scan scan) {
assert scan.forNamespace().isPresent();
return Scan.newBuilder(scan).namespace(namespacePrefix + scan.forNamespace().get()).build();
}
}