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The PGAdapter server implements the PostgreSQL wire-protocol, but sends all received statements
to a Cloud Spanner database instead of a PostgreSQL database. The Cloud Spanner database must
have been created to use the PostgreSQL dialect. See https://cloud.google.com/spanner/docs/quickstart-console#postgresql
for more information on how to create PostgreSQL dialect databases on Cloud Spanner.
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// Copyright 2024 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.cloud.spanner.pgadapter.statements;
import com.google.cloud.spanner.Statement;
import com.google.cloud.spanner.connection.AbstractStatementParser.ParsedStatement;
import com.google.cloud.spanner.connection.AbstractStatementParser.StatementType;
import com.google.cloud.spanner.connection.StatementResult;
import com.google.cloud.spanner.pgadapter.ConnectionHandler;
import com.google.cloud.spanner.pgadapter.error.PGExceptionFactory;
import com.google.cloud.spanner.pgadapter.error.SQLState;
import com.google.cloud.spanner.pgadapter.metadata.OptionsMetadata;
import com.google.cloud.spanner.pgadapter.statements.BackendConnection.ConnectionState;
import com.google.cloud.spanner.pgadapter.statements.BackendConnection.NoResult;
import com.google.cloud.spanner.pgadapter.statements.DiscardStatement.ParsedDiscardStatement.DiscardType;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.common.util.concurrent.Futures;
import java.util.List;
import java.util.concurrent.Future;
public class DiscardStatement extends IntermediatePortalStatement {
static final class ParsedDiscardStatement {
enum DiscardType {
PLANS,
SEQUENCES,
TEMPORARY,
ALL,
}
final DiscardType type;
private ParsedDiscardStatement(DiscardType type) {
this.type = type;
}
}
private final ParsedDiscardStatement discardStatement;
public DiscardStatement(
ConnectionHandler connectionHandler,
OptionsMetadata options,
String name,
ParsedStatement parsedStatement,
Statement originalStatement) {
super(
name,
new IntermediatePreparedStatement(
connectionHandler,
options,
name,
NO_PARAMETER_TYPES,
parsedStatement,
originalStatement),
NO_PARAMS,
ImmutableList.of(),
ImmutableList.of());
this.discardStatement = parse(originalStatement.getSql());
}
@Override
public String getCommandTag() {
return "DISCARD";
}
@Override
public StatementType getStatementType() {
return StatementType.CLIENT_SIDE;
}
@Override
public void executeAsync(BackendConnection backendConnection) {
this.executed = true;
try {
switch (discardStatement.type) {
case ALL:
if (backendConnection.getConnectionState() == ConnectionState.TRANSACTION) {
setFutureStatementResult(
Futures.immediateFailedFuture(
PGExceptionFactory.newPGException(
"DISCARD ALL cannot run inside a transaction block",
SQLState.ActiveSqlTransaction)));
return;
}
backendConnection.getSessionState().resetAll();
connectionHandler.closeAllStatements();
break;
case PLANS:
case SEQUENCES:
case TEMPORARY:
default:
// The default is no-op as PGAdapter does not support clearing plans, sequences or
// temporary tables.
}
} catch (Exception exception) {
setFutureStatementResult(Futures.immediateFailedFuture(exception));
return;
}
setFutureStatementResult(Futures.immediateFuture(new NoResult()));
}
@Override
public Future describeAsync(BackendConnection backendConnection) {
// Return null to indicate that this DISCARD statement does not return any
// RowDescriptionResponse.
return Futures.immediateFuture(null);
}
@Override
public IntermediatePortalStatement createPortal(
String name,
byte[][] parameters,
List parameterFormatCodes,
List resultFormatCodes) {
// DISCARD does not support binding any parameters, so we just return the same statement.
return this;
}
static ParsedDiscardStatement parse(String sql) {
Preconditions.checkNotNull(sql);
SimpleParser parser = new SimpleParser(sql);
if (!parser.eatKeyword("discard")) {
throw PGExceptionFactory.newPGException("not a valid DISCARD statement: " + sql);
}
DiscardType type;
if (parser.eatKeyword("all")) {
type = DiscardType.ALL;
} else if (parser.eatKeyword("plans")) {
type = DiscardType.PLANS;
} else if (parser.eatKeyword("sequences")) {
type = DiscardType.SEQUENCES;
} else if (parser.eatKeyword("temp") || parser.eatKeyword("temporary")) {
type = DiscardType.TEMPORARY;
} else {
throw PGExceptionFactory.newPGException("Invalid DISCARD statement: " + parser.getSql());
}
parser.throwIfHasMoreTokens();
return new ParsedDiscardStatement(type);
}
}
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