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事务概览

本页介绍了 Spanner 中的事务，并包含用于执行事务的示例代码。

简介

Spanner 中的事务是一组读取和写入，在单个逻辑时间点以原子方式跨列、行和表数据库

Spanner 支持以下事务模式：

锁定读写。这些事务依赖于悲观锁定，并且如果必要的两阶段提交锁定读写事务可能会中止需要应用重试。
只读。这种事务类型可保证多次读取之间的一致性，但禁止写入。默认情况下，只读事务在保证外部一致性的系统选择的时间戳执行，但是也可以配置为在过去的时间戳处读取只读事务不需要提交，也不会锁定。此外，只读事务可能会等待正在进行的写入完成运行状态。
分区 DML。此事务类型执行数据操纵语言 (DML) 语句作为分区 DML。分区 DML 专为批量更新和删除（尤其是定期清理和回填）而设计。如果您需要提交大量盲目写入，但不需要原子事务，则可以使用批量写入来批量修改 Spanner 表。如需了解详情，请参阅使用批量写入修改数据。

本页面介绍 Google Cloud 中事务的常规属性和语义， Spanner，并引入了读写、只读和分区 DML Spanner 中的事务接口。

读写事务

在下列情况下，应该使用锁定读写事务：

如果您执行的写入操作依赖于一项或多项读取的结果，则应该在同一项读写事务中执行读写。
- 例如：银行账户 A 的余额翻倍。对 A 余额的读取应该与写入在同一项事务中进行，以将余额替换为双倍值。
如果您执行的一项或多项写入需要以原子方式提交应该在同一项读写事务中执行这些写入操作。
- 例如：将 200 美元从账户 A 转到账户 B。两项写入（一项写入是让账户 A 减少 200 美元，另一项写入是让账户 B 增加 200美元）和初始账户余额读取应在同一项事务中进行。
如果根据一项或多项读取的结果，您可能会执行一项或多项写入，那么您就应该在同一项读写事务中执行这些读写（哪怕您最终没有执行写入）。
- 例如：如果银行账户 A 的当前余额大于 500 美元，则将账户 A 中的 200 美元转到银行账户 B。您的事务应包含对账户 A 余额的读取和一个包含写入的条件语句。

在以下情况下，不应该使用锁定读写事务：

如果您只执行读取，并且可以使用单次读取方法来表达您的读取，则应该使用该单次读取方法或只读事务。与读写事务不同，单次读取不会锁定。

属性

Spanner 中的读写事务会执行一组读写操作在单个逻辑时间点以原子方式呈现。此外，读写事务执行的时间戳与挂钟时间匹配，并且序列化顺序与时间戳顺序匹配。

为什么使用读写事务？读写事务可提供 ACID 属性（事实上，Spanner 支持读写与传统 ACID 相比，事务能够提供更强大的保证；请参阅语义部分）。

隔离

以下是读写和只读的隔离属性事务。

读写事务

以下是您在成功提交事务，该事务包含一系列读取（或查询）和写入：

事务中的所有读取返回的值反映一致的在事务的提交时间戳截取的快照。
在提交时仍存在空行或范围。
事务内的所有写入都在事务的提交时间戳提交。
在事务之后，写入对于任何事务都不可见投入。

某些 Spanner 客户端驱动程序包含用于遮盖的事务重试逻辑暂时性错误，它们通过重新运行事务并验证客户端观测到的数据

其结果是所有读写操作似乎是在（无论是从事务本身还是从事务并分析 Spanner 数据库的其他读取者和写入者的角度。换句话说，读取和写入最终发生在相同的时间戳（有关说明，请参阅下面的可序列化和外部一致性部分）。

只读事务

对于只执行读取的读写事务，其保证是相似的：该事务中的所有读取都返回来自同一时间戳的数据，即使行不存在也是如此。一个不同点在于，如果您读取了数据，稍后又提交了没有任何写入的读写事务，则不能保证在读取之后与提交之前的这段时间内，数据库中的数据没有发生变化。如果您想知道自从您上次读取数据后数据是否发生了变化，最好的方法是再次读取它（在读写事务中或者使用强读）。另外，为了提高效率，如果您事先知道您只执行读取而不写入，则应该使用只读事务而不是读写事务。

原子性、一致性、持久性

除了隔离属性外，Spanner 还提供原子性（如果事务提交中的任何写入，它们都会提交）、一致性（数据库在事务后保持不变的状态）和持久性（提交的数据会保持承诺状态。）

这些特性的优势

得益于 Cloud Spanner 的这些特性，应用开发者可以专注于每项事务本身的正确性，而不必想方设法让其执行不受可能同时执行的其他事务干扰。

界面

Spanner 客户端库提供了一个用于执行正文的接口，读写事务上下文中的工作，以及针对事务重试中止。以下提供一些背景信息来解释这一点：Spanner 可能要多次尝试事务，然后才能提交。例如：如果两个事务都试图同时处理数据，导致死锁，Spanner 会取消其中一个事务，以便另一个事务可以进步。（较为罕见的是，Spanner 中的瞬态事件会导致某些事务取消。）由于事务具有原子性，被中止的事务不会对数据库有可见的影响。因此，应该不断重新尝试执行这些事务，直至成功。

在 Spanner 客户端库中使用事务时，您需要定义事务的正文（即，要对一个或多个实例执行的读取和写入数据库中的表）以函数对象的形式指定。在后台，Spanner 客户端库会反复运行该函数，直到事务得到提交或遇到不可重试的错误。

示例

假设您向“架构和数据模型”页面中所示的 Albums 表添加了 MarketingBudget 列：

CREATE TABLE Albums (
  SingerId        INT64 NOT NULL,
  AlbumId         INT64 NOT NULL,
  AlbumTitle      STRING(MAX),
  MarketingBudget INT64
) PRIMARY KEY (SingerId, AlbumId);

您的营销部门决定为专辑 Albums (1, 1) 做市场推广，要求您从 Albums (2, 2) 的预算中划拨 200000 美元（但前提是该专辑的预算资金充裕）。您应该为此操作使用锁定读写事务，因为该事务可能会根据读取结果执行写入。

下面演示了如何执行读写事务：

C++

void ReadWriteTransaction(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;
  using ::google::cloud::StatusOr;

  // A helper to read a single album MarketingBudget.
  auto get_current_budget =
      [](spanner::Client client, spanner::Transaction txn,
         std::int64_t singer_id,
         std::int64_t album_id) -> StatusOr<std::int64_t> {
    auto key = spanner::KeySet().AddKey(spanner::MakeKey(singer_id, album_id));
    auto rows = client.Read(std::move(txn), "Albums", std::move(key),
                            {"MarketingBudget"});
    using RowType = std::tuple<std::int64_t>;
    auto row = spanner::GetSingularRow(spanner::StreamOf<RowType>(rows));
    if (!row) return std::move(row).status();
    return std::get<0>(*std::move(row));
  };

  auto commit = client.Commit(
      [&client, &get_current_budget](
          spanner::Transaction const& txn) -> StatusOr<spanner::Mutations> {
        auto b1 = get_current_budget(client, txn, 1, 1);
        if (!b1) return std::move(b1).status();
        auto b2 = get_current_budget(client, txn, 2, 2);
        if (!b2) return std::move(b2).status();
        std::int64_t transfer_amount = 200000;

        return spanner::Mutations{
            spanner::UpdateMutationBuilder(
                "Albums", {"SingerId", "AlbumId", "MarketingBudget"})
                .EmplaceRow(1, 1, *b1 + transfer_amount)
                .EmplaceRow(2, 2, *b2 - transfer_amount)
                .Build()};
      });

  if (!commit) throw std::move(commit).status();
  std::cout << "Transfer was successful [spanner_read_write_transaction]\n";
}

C#


using Google.Cloud.Spanner.Data;
using System;
using System.Threading.Tasks;
using System.Transactions;

public class ReadWriteWithTransactionAsyncSample
{
    public async Task<int> ReadWriteWithTransactionAsync(string projectId, string instanceId, string databaseId)
    {
        // This sample transfers 200,000 from the MarketingBudget
        // field of the second Album to the first Album. Make sure to run
        // the Add Column and Write Data To New Column samples first,
        // in that order.

        string connectionString = $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}";

        using TransactionScope scope = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled);
        decimal transferAmount = 200000;
        decimal secondBudget = 0;
        decimal firstBudget = 0;

        using var connection = new SpannerConnection(connectionString);
        using var cmdLookup1 = connection.CreateSelectCommand("SELECT * FROM Albums WHERE SingerId = 2 AND AlbumId = 2");

        using (var reader = await cmdLookup1.ExecuteReaderAsync())
        {
            while (await reader.ReadAsync())
            {
                // Read the second album's budget.
                secondBudget = reader.GetFieldValue<decimal>("MarketingBudget");
                // Confirm second Album's budget is sufficient and
                // if not raise an exception. Raising an exception
                // will automatically roll back the transaction.
                if (secondBudget < transferAmount)
                {
                    throw new Exception($"The second album's budget {secondBudget} is less than the amount to transfer.");
                }
            }
        }

        // Read the first album's budget.
        using var cmdLookup2 = connection.CreateSelectCommand("SELECT * FROM Albums WHERE SingerId = 1 and AlbumId = 1");
        using (var reader = await cmdLookup2.ExecuteReaderAsync())
        {
            while (await reader.ReadAsync())
            {
                firstBudget = reader.GetFieldValue<decimal>("MarketingBudget");
            }
        }

        // Specify update command parameters.
        using var cmdUpdate = connection.CreateUpdateCommand("Albums", new SpannerParameterCollection
        {
            { "SingerId", SpannerDbType.Int64 },
            { "AlbumId", SpannerDbType.Int64 },
            { "MarketingBudget", SpannerDbType.Int64 },
        });

        // Update second album to remove the transfer amount.
        secondBudget -= transferAmount;
        cmdUpdate.Parameters["SingerId"].Value = 2;
        cmdUpdate.Parameters["AlbumId"].Value = 2;
        cmdUpdate.Parameters["MarketingBudget"].Value = secondBudget;
        var rowCount = await cmdUpdate.ExecuteNonQueryAsync();

        // Update first album to add the transfer amount.
        firstBudget += transferAmount;
        cmdUpdate.Parameters["SingerId"].Value = 1;
        cmdUpdate.Parameters["AlbumId"].Value = 1;
        cmdUpdate.Parameters["MarketingBudget"].Value = firstBudget;
        rowCount += await cmdUpdate.ExecuteNonQueryAsync();
        scope.Complete();
        Console.WriteLine("Transaction complete.");
        return rowCount;
    }
}

Go


import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/spanner"
)

func writeWithTransaction(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
		getBudget := func(key spanner.Key) (int64, error) {
			row, err := txn.ReadRow(ctx, "Albums", key, []string{"MarketingBudget"})
			if err != nil {
				return 0, err
			}
			var budget int64
			if err := row.Column(0, &budget); err != nil {
				return 0, err
			}
			return budget, nil
		}
		album2Budget, err := getBudget(spanner.Key{2, 2})
		if err != nil {
			return err
		}
		const transferAmt = 200000
		if album2Budget >= transferAmt {
			album1Budget, err := getBudget(spanner.Key{1, 1})
			if err != nil {
				return err
			}
			album1Budget += transferAmt
			album2Budget -= transferAmt
			cols := []string{"SingerId", "AlbumId", "MarketingBudget"}
			txn.BufferWrite([]*spanner.Mutation{
				spanner.Update("Albums", cols, []interface{}{1, 1, album1Budget}),
				spanner.Update("Albums", cols, []interface{}{2, 2, album2Budget}),
			})
			fmt.Fprintf(w, "Moved %d from Album2's MarketingBudget to Album1's.", transferAmt)
		}
		return nil
	})
	return err
}

Java

static void writeWithTransaction(DatabaseClient dbClient) {
  dbClient
      .readWriteTransaction()
      .run(transaction -> {
        // Transfer marketing budget from one album to another. We do it in a transaction to
        // ensure that the transfer is atomic.
        Struct row =
            transaction.readRow("Albums", Key.of(2, 2), Arrays.asList("MarketingBudget"));
        long album2Budget = row.getLong(0);
        // Transaction will only be committed if this condition still holds at the time of
        // commit. Otherwise it will be aborted and the callable will be rerun by the
        // client library.
        long transfer = 200000;
        if (album2Budget >= transfer) {
          long album1Budget =
              transaction
                  .readRow("Albums", Key.of(1, 1), Arrays.asList("MarketingBudget"))
                  .getLong(0);
          album1Budget += transfer;
          album2Budget -= transfer;
          transaction.buffer(
              Mutation.newUpdateBuilder("Albums")
                  .set("SingerId")
                  .to(1)
                  .set("AlbumId")
                  .to(1)
                  .set("MarketingBudget")
                  .to(album1Budget)
                  .build());
          transaction.buffer(
              Mutation.newUpdateBuilder("Albums")
                  .set("SingerId")
                  .to(2)
                  .set("AlbumId")
                  .to(2)
                  .set("MarketingBudget")
                  .to(album2Budget)
                  .build());
        }
        return null;
      });
}

Node.js

// This sample transfers 200,000 from the MarketingBudget field
// of the second Album to the first Album, as long as the second
// Album has enough money in its budget. Make sure to run the
// addColumn and updateData samples first (in that order).

// Imports the Google Cloud client library
const {Spanner} = require('@google-cloud/spanner');

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// const projectId = 'my-project-id';
// const instanceId = 'my-instance';
// const databaseId = 'my-database';

// Creates a client
const spanner = new Spanner({
  projectId: projectId,
});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

const transferAmount = 200000;

database.runTransaction(async (err, transaction) => {
  if (err) {
    console.error(err);
    return;
  }
  let firstBudget, secondBudget;
  const queryOne = {
    columns: ['MarketingBudget'],
    keys: [[2, 2]], // SingerId: 2, AlbumId: 2
  };

  const queryTwo = {
    columns: ['MarketingBudget'],
    keys: [[1, 1]], // SingerId: 1, AlbumId: 1
  };

  Promise.all([
    // Reads the second album's budget
    transaction.read('Albums', queryOne).then(results => {
      // Gets second album's budget
      const rows = results[0].map(row => row.toJSON());
      secondBudget = rows[0].MarketingBudget;
      console.log(`The second album's marketing budget: ${secondBudget}`);

      // Makes sure the second album's budget is large enough
      if (secondBudget < transferAmount) {
        throw new Error(
          `The second album's budget (${secondBudget}) is less than the transfer amount (${transferAmount}).`
        );
      }
    }),

    // Reads the first album's budget
    transaction.read('Albums', queryTwo).then(results => {
      // Gets first album's budget
      const rows = results[0].map(row => row.toJSON());
      firstBudget = rows[0].MarketingBudget;
      console.log(`The first album's marketing budget: ${firstBudget}`);
    }),
  ])
    .then(() => {
      console.log(firstBudget, secondBudget);
      // Transfers the budgets between the albums
      firstBudget += transferAmount;
      secondBudget -= transferAmount;

      console.log(firstBudget, secondBudget);

      // Updates the database
      // Note: Cloud Spanner interprets Node.js numbers as FLOAT64s, so they
      // must be converted (back) to strings before being inserted as INT64s.
      transaction.update('Albums', [
        {
          SingerId: '1',
          AlbumId: '1',
          MarketingBudget: firstBudget.toString(),
        },
        {
          SingerId: '2',
          AlbumId: '2',
          MarketingBudget: secondBudget.toString(),
        },
      ]);
    })
    .then(() => {
      // Commits the transaction and send the changes to the database
      return transaction.commit();
    })
    .then(() => {
      console.log(
        `Successfully executed read-write transaction to transfer ${transferAmount} from Album 2 to Album 1.`
      );
    })
    .catch(err => {
      console.error('ERROR:', err);
    })
    .then(() => {
      transaction.end();
      // Closes the database when finished
      return database.close();
    });
});

PHP

use Google\Cloud\Spanner\SpannerClient;
use Google\Cloud\Spanner\Transaction;
use UnexpectedValueException;

/**
 * Performs a read-write transaction to update two sample records in the
 * database.
 *
 * This will transfer 200,000 from the `MarketingBudget` field for the second
 * Album to the first Album. If the `MarketingBudget` for the second Album is
 * too low, it will raise an exception.
 *
 * Before running this sample, you will need to run the `update_data` sample
 * to populate the fields.
 * Example:
 * ```
 * read_write_transaction($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function read_write_transaction(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $database->runTransaction(function (Transaction $t) use ($spanner) {
        $transferAmount = 200000;

        // Read the second album's budget.
        $secondAlbumKey = [2, 2];
        $secondAlbumKeySet = $spanner->keySet(['keys' => [$secondAlbumKey]]);
        $secondAlbumResult = $t->read(
            'Albums',
            $secondAlbumKeySet,
            ['MarketingBudget'],
            ['limit' => 1]
        );

        $firstRow = $secondAlbumResult->rows()->current();
        $secondAlbumBudget = $firstRow['MarketingBudget'];
        if ($secondAlbumBudget < $transferAmount) {
            // Throwing an exception will automatically roll back the transaction.
            throw new UnexpectedValueException(
                'The second album\'s budget is lower than the transfer amount: ' . $transferAmount
            );
        }

        $firstAlbumKey = [1, 1];
        $firstAlbumKeySet = $spanner->keySet(['keys' => [$firstAlbumKey]]);
        $firstAlbumResult = $t->read(
            'Albums',
            $firstAlbumKeySet,
            ['MarketingBudget'],
            ['limit' => 1]
        );

        // Read the first album's budget.
        $firstRow = $firstAlbumResult->rows()->current();
        $firstAlbumBudget = $firstRow['MarketingBudget'];

        // Update the budgets.
        $secondAlbumBudget -= $transferAmount;
        $firstAlbumBudget += $transferAmount;
        printf('Setting first album\'s budget to %s and the second album\'s ' .
            'budget to %s.' . PHP_EOL, $firstAlbumBudget, $secondAlbumBudget);

        // Update the rows.
        $t->updateBatch('Albums', [
            ['SingerId' => 1, 'AlbumId' => 1, 'MarketingBudget' => $firstAlbumBudget],
            ['SingerId' => 2, 'AlbumId' => 2, 'MarketingBudget' => $secondAlbumBudget],
        ]);

        // Commit the transaction!
        $t->commit();

        print('Transaction complete.' . PHP_EOL);
    });
}

Python

def read_write_transaction(instance_id, database_id):
    """Performs a read-write transaction to update two sample records in the
    database.

    This will transfer 200,000 from the `MarketingBudget` field for the second
    Album to the first Album. If the `MarketingBudget` is too low, it will
    raise an exception.

    Before running this sample, you will need to run the `update_data` sample
    to populate the fields.
    """
    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)

    def update_albums(transaction):
        # Read the second album budget.
        second_album_keyset = spanner.KeySet(keys=[(2, 2)])
        second_album_result = transaction.read(
            table="Albums",
            columns=("MarketingBudget",),
            keyset=second_album_keyset,
            limit=1,
        )
        second_album_row = list(second_album_result)[0]
        second_album_budget = second_album_row[0]

        transfer_amount = 200000

        if second_album_budget < transfer_amount:
            # Raising an exception will automatically roll back the
            # transaction.
            raise ValueError("The second album doesn't have enough funds to transfer")

        # Read the first album's budget.
        first_album_keyset = spanner.KeySet(keys=[(1, 1)])
        first_album_result = transaction.read(
            table="Albums",
            columns=("MarketingBudget",),
            keyset=first_album_keyset,
            limit=1,
        )
        first_album_row = list(first_album_result)[0]
        first_album_budget = first_album_row[0]

        # Update the budgets.
        second_album_budget -= transfer_amount
        first_album_budget += transfer_amount
        print(
            "Setting first album's budget to {} and the second album's "
            "budget to {}.".format(first_album_budget, second_album_budget)
        )

        # Update the rows.
        transaction.update(
            table="Albums",
            columns=("SingerId", "AlbumId", "MarketingBudget"),
            values=[(1, 1, first_album_budget), (2, 2, second_album_budget)],
        )

    database.run_in_transaction(update_albums)

    print("Transaction complete.")

Ruby

# project_id  = "Your Google Cloud project ID"
# instance_id = "Your Spanner instance ID"
# database_id = "Your Spanner database ID"

require "google/cloud/spanner"

spanner         = Google::Cloud::Spanner.new project: project_id
client          = spanner.client instance_id, database_id
transfer_amount = 200_000

client.transaction do |transaction|
  first_album  = transaction.read("Albums", [:MarketingBudget], keys: [[1, 1]]).rows.first
  second_album = transaction.read("Albums", [:MarketingBudget], keys: [[2, 2]]).rows.first

  raise "The second album does not have enough funds to transfer" if second_album[:MarketingBudget] < transfer_amount

  new_first_album_budget  = first_album[:MarketingBudget] + transfer_amount
  new_second_album_budget = second_album[:MarketingBudget] - transfer_amount

  transaction.update "Albums", [
    { SingerId: 1, AlbumId: 1, MarketingBudget: new_first_album_budget  },
    { SingerId: 2, AlbumId: 2, MarketingBudget: new_second_album_budget }
  ]
end

puts "Transaction complete"

语义

可序列化和外部一致性

Spanner 提供“可序列化”，这意味着所有事务即使某些读取、写入、不同事务的其他操作实际上是并行发生的。 Spanner 分配的提交时间戳反映了提交的顺序实现此属性事实上，Spanner 提供了比可序列化更强的保证称为外部一致性：事务提交至提交时间戳中反映的顺序，这些提交时间戳反映的是实时数据，因此您可以将其与您的手表进行比较。事务中的读取可以看到在该事务提交之前所提交的所有内容，而在该事务提交之后开始的所有操作都可以看到该事务中的写入。

例如，假设要执行两项事务，如下图所示：

蓝色事 Txn1 读取数据 A，缓冲对 A 的写入，然后成功提交。绿色事务 Txn2 在 Txn1 之后开始，读取数据 B，然后读取数据 A。由于 Txn2 在 Txn1 提交其对 A 的写入之后才读取 A 的值，因此 Txn2 会看到 Txn1 写入到 A 这一效果，即使 Txn2 实际上是在 Txn1 完成之前开始的也是如此。

尽管 Txn1 和 Txn2 的执行时间部分重叠，但它们的提交时间戳 c1 和 c2 都遵循线性的事务顺序，也就是说，Txn1 的所有读写效果看起来发生在单个时间点 (c1)，而 Txn2 的所有读写操作看起来也发生在单个时间点 (c2)。此外，c1 < c2（由于 Txn1 和 Txn2 均提交了写入，因此这一点具有保证；即使写入发生在不同的机器上也是如此），其遵循 Txn1 在 Txn2 之前发生这一顺序（但是，如果 Txn2 只在事务中执行读取，则 c1 <= c2）。

读取操作会观察到提交历史记录的前缀；如果其可看到 Txn2 的效果，则也会看到 Txn1 的效果。所有成功提交的事务都具有此特性。

读写保证

如果运行事务的调用失败，那么您所获得的读写保证取决于底层的提交调用是因什么错误而失败。

例如，“未找到行”或“行已存在”等错误意味着写入缓冲的数据变动时遇到了一些错误，例如客户端试图更新的行不存在。在这种情况下，读取保证一致，写入不会得到执行，行不存在的情形也保证与读取一致。

取消事务操作

用户可以随时取消异步读取操作（例如，当更高级层的操作被取消或您根据初始读取结果而决定停止读取时），这样做不会影响事务内的任何其他现有操作。

但是，即使您尝试取消读取，Spanner 也不会可以保证读取操作确实会取消。在您请求取消读取之后，该读取仍可能会成功完成或因其他原因（例如中止）而失败。此外，取消的读取可能实际上会向您返回一些结果，并且那些可能不完整的结果将作为事务提交的一部分进行验证。

请注意，与读取不同，如果取消事务提交操作，将导致事务中止（除非事务已经提交或因其他原因而失败）。

性能

锁定

Spanner 允许多个客户端同时与同一个数据库。为了确保多个并发任务的一致性因此 Spanner 将共享锁和独占模式来控制对数据的访问。当您在集群内 Spanner 会获取共享读取锁，这使得以确保在事务准备好提交之前仍然可以访问数据。当系统提交您的事务并执行写入时，事务将尝试升级到独占锁定。它会阻止对数据施加新的共享读取锁定，并等待现有的共享读取锁定被清除，然后施加独占锁定，以独占数据访问权。

有关锁定的注意事项：

锁定是在行和列的粒度进行的。如果事务 T1 锁定了行“foo”的“A”列，并且事务 T2 想要写入行“foo”的“B”列，则不存在冲突。
如果对某项数据的写入操作不会读取相应数据（亦称“盲写”），则这些写入不会与同一项数据的其他盲写发生冲突（每项写入的提交时间戳决定其应用于数据库的顺序）。如此一来，Spanner 只需进行升级独占锁定。其他情况 Spanner 使用一种称为写入方共享锁定的共享锁。
在读写事务中执行行查询时，请使用二级索引将扫描的行限制为较小的范围。这会使 Spanner 锁定的数字更少行，允许对表外的行进行并发修改范围。
不应使用锁定来确保对外部资源进行独占访问 Spanner。事务可能由于多种原因而被取消，例如，当允许数据在实例的计算资源无论是通过应用代码显式重试事务，还是重试事务也可以由客户端代码（例如 Spanner JDBC 驱动程序，它只是可以保证在实际提交尝试期间持有锁。
您可以使用锁定统计信息内省工具来调查数据库中的锁定冲突。

死锁检测

Spanner 会检测多个事务何时可能发生死锁，以及强制取消除一项事务之外的所有事务。例如，设想以下场景：事务 Txn1 持有记录 A 的锁定，并正在等待记录 B 的锁定解除，而 Txn2 持有记录 B 的锁定并正在等待记录 A 的锁定解除。在这种情况下，取得进展的唯一方法是放弃其中一项事务，以便释放其锁定，从而允许另一项事务继续进行。

Spanner 使用标准的“受伤-等待”算法来处理死锁检测。Spanner 会在后台跟踪每个查询的存在时间，事务。并允许较早的事务中止较晚的事务（其中，“较早”意味着事务的最早读取、查询或提交开始的时间更早）。

通过优先处理较早的事务，Spanner 可确保事务最终有机会在过期后获取锁具有比其他事务更高的优先级。例如，获取了读取方共享锁定的事务可被需要写入方共享锁定的较早事务中止。

分布式执行

Spanner 可以对跨多个服务器的数据运行事务。与单服务器事务相比，这项功能会导致一定的性能损失。

哪些类型的事务可能是分布式的？Spanner 的底层机制可以将数据库中的行划分到多个服务器上。某行和交错表中的相应行通常由同一台服务器处理，就像同一个表中键邻近的两行。Spanner 可以在不同服务器上跨行执行事务；但作为一般来说，影响多个位于同一位置的行的事务比影响分散存储在数据库中的许多行的事务，或大型表格

Spanner 中最高效的事务仅包括应该以原子方式应用的写入。当所有读取和写入操作均访问位于键空间同一部分的数据时，事务处理速度最快。

只读事务

除了锁定读写事务外，Spanner 还提供了只读事务。

当您需要在同一时间戳执行多项读取时，请使用只读事务。如果您可以使用 Spanner 的某个单次读取方法，则应使用单一读取方法使用这种单次读取调用的性能应该与在只读事务中执行单次读取的性能相当。

如果要读取大量数据，请考虑使用分区来并行读取数据。

由于只读事务不会写入，它们不会持有锁定，也不会阻止其他事务。只读事务会观察到一致的事务提交历史记录前缀，因此您的应用始终可获得一致的数据。

属性

无论是从只读事务本身的角度，还是从 Spanner 数据库中其他读取方和写入方的角度来看，Spanner 只读事务都是在单个逻辑时间点执行一组读取。这意味着，只读事务始终可在事务历史记录的选定点处观察到一致的数据库状态。

界面

Spanner 提供了一个接口，用于在只读事务的上下文，在事务中止时重试。

示例

下面演示了如何使用只读事务，为同一时间戳的两次读取获取一致的数据：

C++

void ReadOnlyTransaction(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;
  auto read_only = spanner::MakeReadOnlyTransaction();

  spanner::SqlStatement select(
      "SELECT SingerId, AlbumId, AlbumTitle FROM Albums");
  using RowType = std::tuple<std::int64_t, std::int64_t, std::string>;

  // Read#1.
  auto rows1 = client.ExecuteQuery(read_only, select);
  std::cout << "Read 1 results\n";
  for (auto& row : spanner::StreamOf<RowType>(rows1)) {
    if (!row) throw std::move(row).status();
    std::cout << "SingerId: " << std::get<0>(*row)
              << " AlbumId: " << std::get<1>(*row)
              << " AlbumTitle: " << std::get<2>(*row) << "\n";
  }
  // Read#2. Even if changes occur in-between the reads the transaction ensures
  // that Read #1 and Read #2 return the same data.
  auto rows2 = client.ExecuteQuery(read_only, select);
  std::cout << "Read 2 results\n";
  for (auto& row : spanner::StreamOf<RowType>(rows2)) {
    if (!row) throw std::move(row).status();
    std::cout << "SingerId: " << std::get<0>(*row)
              << " AlbumId: " << std::get<1>(*row)
              << " AlbumTitle: " << std::get<2>(*row) << "\n";
  }
}

C#


using Google.Cloud.Spanner.Data;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Transactions;

public class QueryDataWithTransactionAsyncSample
{
    public class Album
    {
        public int SingerId { get; set; }
        public int AlbumId { get; set; }
        public string AlbumTitle { get; set; }
    }

    public async Task<List<Album>> QueryDataWithTransactionAsync(string projectId, string instanceId, string databaseId)
    {
        string connectionString = $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}";

        var albums = new List<Album>();
        using TransactionScope scope = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled);
        using var connection = new SpannerConnection(connectionString);

        // Opens the connection so that the Spanner transaction included in the TransactionScope
        // is read-only TimestampBound.Strong.
        await connection.OpenAsync(AmbientTransactionOptions.ForTimestampBoundReadOnly(), default);
        using var cmd = connection.CreateSelectCommand("SELECT SingerId, AlbumId, AlbumTitle FROM Albums");

        // Read #1.
        using (var reader = await cmd.ExecuteReaderAsync())
        {
            while (await reader.ReadAsync())
            {
                Console.WriteLine("SingerId : " + reader.GetFieldValue<string>("SingerId")
                    + " AlbumId : " + reader.GetFieldValue<string>("AlbumId")
                    + " AlbumTitle : " + reader.GetFieldValue<string>("AlbumTitle"));
            }
        }

        // Read #2. Even if changes occur in-between the reads,
        // the transaction ensures that Read #1 and Read #2
        // return the same data.
        using (var reader = await cmd.ExecuteReaderAsync())
        {
            while (await reader.ReadAsync())
            {
                albums.Add(new Album
                {
                    AlbumId = reader.GetFieldValue<int>("AlbumId"),
                    SingerId = reader.GetFieldValue<int>("SingerId"),
                    AlbumTitle = reader.GetFieldValue<string>("AlbumTitle")
                });
            }
        }
        scope.Complete();
        Console.WriteLine("Transaction complete.");
        return albums;
    }
}

Go


import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/spanner"
	"google.golang.org/api/iterator"
)

func readOnlyTransaction(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	ro := client.ReadOnlyTransaction()
	defer ro.Close()
	stmt := spanner.Statement{SQL: `SELECT SingerId, AlbumId, AlbumTitle FROM Albums`}
	iter := ro.Query(ctx, stmt)
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			return err
		}
		var singerID int64
		var albumID int64
		var albumTitle string
		if err := row.Columns(&singerID, &albumID, &albumTitle); err != nil {
			return err
		}
		fmt.Fprintf(w, "%d %d %s\n", singerID, albumID, albumTitle)
	}

	iter = ro.Read(ctx, "Albums", spanner.AllKeys(), []string{"SingerId", "AlbumId", "AlbumTitle"})
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			return nil
		}
		if err != nil {
			return err
		}
		var singerID int64
		var albumID int64
		var albumTitle string
		if err := row.Columns(&singerID, &albumID, &albumTitle); err != nil {
			return err
		}
		fmt.Fprintf(w, "%d %d %s\n", singerID, albumID, albumTitle)
	}
}

Java

static void readOnlyTransaction(DatabaseClient dbClient) {
  // ReadOnlyTransaction must be closed by calling close() on it to release resources held by it.
  // We use a try-with-resource block to automatically do so.
  try (ReadOnlyTransaction transaction = dbClient.readOnlyTransaction()) {
    ResultSet queryResultSet =
        transaction.executeQuery(
            Statement.of("SELECT SingerId, AlbumId, AlbumTitle FROM Albums"));
    while (queryResultSet.next()) {
      System.out.printf(
          "%d %d %s\n",
          queryResultSet.getLong(0), queryResultSet.getLong(1), queryResultSet.getString(2));
    }
    try (ResultSet readResultSet =
        transaction.read(
            "Albums", KeySet.all(), Arrays.asList("SingerId", "AlbumId", "AlbumTitle"))) {
      while (readResultSet.next()) {
        System.out.printf(
            "%d %d %s\n",
            readResultSet.getLong(0), readResultSet.getLong(1), readResultSet.getString(2));
      }
    }
  }
}

Node.js

// Imports the Google Cloud client library
const {Spanner} = require('@google-cloud/spanner');

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// const projectId = 'my-project-id';
// const instanceId = 'my-instance';
// const databaseId = 'my-database';

// Creates a client
const spanner = new Spanner({
  projectId: projectId,
});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

// Gets a transaction object that captures the database state
// at a specific point in time
database.getSnapshot(async (err, transaction) => {
  if (err) {
    console.error(err);
    return;
  }
  const queryOne = 'SELECT SingerId, AlbumId, AlbumTitle FROM Albums';

  try {
    // Read #1, using SQL
    const [qOneRows] = await transaction.run(queryOne);

    qOneRows.forEach(row => {
      const json = row.toJSON();
      console.log(
        `SingerId: ${json.SingerId}, AlbumId: ${json.AlbumId}, AlbumTitle: ${json.AlbumTitle}`
      );
    });

    const queryTwo = {
      columns: ['SingerId', 'AlbumId', 'AlbumTitle'],
    };

    // Read #2, using the `read` method. Even if changes occur
    // in-between the reads, the transaction ensures that both
    // return the same data.
    const [qTwoRows] = await transaction.read('Albums', queryTwo);

    qTwoRows.forEach(row => {
      const json = row.toJSON();
      console.log(
        `SingerId: ${json.SingerId}, AlbumId: ${json.AlbumId}, AlbumTitle: ${json.AlbumTitle}`
      );
    });

    console.log('Successfully executed read-only transaction.');
  } catch (err) {
    console.error('ERROR:', err);
  } finally {
    transaction.end();
    // Close the database when finished.
    await database.close();
  }
});

PHP

use Google\Cloud\Spanner\SpannerClient;

/**
 * Reads data inside of a read-only transaction.
 *
 * Within the read-only transaction, or "snapshot", the application sees
 * consistent view of the database at a particular timestamp.
 * Example:
 * ```
 * read_only_transaction($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function read_only_transaction(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $snapshot = $database->snapshot();
    $results = $snapshot->execute(
        'SELECT SingerId, AlbumId, AlbumTitle FROM Albums'
    );
    print('Results from the first read:' . PHP_EOL);
    foreach ($results as $row) {
        printf('SingerId: %s, AlbumId: %s, AlbumTitle: %s' . PHP_EOL,
            $row['SingerId'], $row['AlbumId'], $row['AlbumTitle']);
    }

    // Perform another read using the `read` method. Even if the data
    // is updated in-between the reads, the snapshot ensures that both
    // return the same data.
    $keySet = $spanner->keySet(['all' => true]);
    $results = $database->read(
        'Albums',
        $keySet,
        ['SingerId', 'AlbumId', 'AlbumTitle']
    );

    print('Results from the second read:' . PHP_EOL);
    foreach ($results->rows() as $row) {
        printf('SingerId: %s, AlbumId: %s, AlbumTitle: %s' . PHP_EOL,
            $row['SingerId'], $row['AlbumId'], $row['AlbumTitle']);
    }
}

Python

def read_only_transaction(instance_id, database_id):
    """Reads data inside of a read-only transaction.

    Within the read-only transaction, or "snapshot", the application sees
    consistent view of the database at a particular timestamp.
    """
    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)

    with database.snapshot(multi_use=True) as snapshot:
        # Read using SQL.
        results = snapshot.execute_sql(
            "SELECT SingerId, AlbumId, AlbumTitle FROM Albums"
        )

        print("Results from first read:")
        for row in results:
            print("SingerId: {}, AlbumId: {}, AlbumTitle: {}".format(*row))

        # Perform another read using the `read` method. Even if the data
        # is updated in-between the reads, the snapshot ensures that both
        # return the same data.
        keyset = spanner.KeySet(all_=True)
        results = snapshot.read(
            table="Albums", columns=("SingerId", "AlbumId", "AlbumTitle"), keyset=keyset
        )

        print("Results from second read:")
        for row in results:
            print("SingerId: {}, AlbumId: {}, AlbumTitle: {}".format(*row))

Ruby

# project_id  = "Your Google Cloud project ID"
# instance_id = "Your Spanner instance ID"
# database_id = "Your Spanner database ID"

require "google/cloud/spanner"

spanner = Google::Cloud::Spanner.new project: project_id
client  = spanner.client instance_id, database_id

client.snapshot do |snapshot|
  snapshot.execute("SELECT SingerId, AlbumId, AlbumTitle FROM Albums").rows.each do |row|
    puts "#{row[:AlbumId]} #{row[:AlbumTitle]} #{row[:SingerId]}"
  end

  # Even if changes occur in-between the reads, the transaction ensures that
  # both return the same data.
  snapshot.read("Albums", [:AlbumId, :AlbumTitle, :SingerId]).rows.each do |row|
    puts "#{row[:AlbumId]} #{row[:AlbumTitle]} #{row[:SingerId]}"
  end
end

分区 DML 事务

通过使用分区数据操纵语言（分区 DML），您可以执行大量的 UPDATE 和 DELETE 语句，并且不会遇到事务限制或锁定整个表。Spanner 对键空间进行分区，并对每个键执行 DML 语句一个单独的读写事务中

您可以在代码中明确创建的读写事务中运行 DML 语句。如需了解详情，请参阅使用 DML。

属性

无论是使用客户端库方法还是使用 Google Cloud CLI，一次只能执行一个分区 DML 语句。

分区事务不支持提交或回滚。Spanner 立即执行和应用 DML 语句。如果取消操作若操作失败，则 Spanner 会取消所有正在执行的并且不会启动任何剩余的分区。Spanner 不会回滚已执行的任何分区。

界面

Spanner 提供了一个用于执行单个分区 DML 的接口声明。

示例

以下代码示例更新 Albums 表的 MarketingBudget 列。

C++

您可以使用 ExecutePartitionedDml() 函数来执行分区 DML 语句。

void DmlPartitionedUpdate(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;
  auto result = client.ExecutePartitionedDml(
      spanner::SqlStatement("UPDATE Albums SET MarketingBudget = 100000"
                            "  WHERE SingerId > 1"));
  if (!result) throw std::move(result).status();
  std::cout << "Updated at least " << result->row_count_lower_bound
            << " row(s) [spanner_dml_partitioned_update]\n";
}

C#

使用 ExecutePartitionedUpdateAsync() 方法来执行分区 DML 语句。


using Google.Cloud.Spanner.Data;
using System;
using System.Threading.Tasks;

public class UpdateUsingPartitionedDmlCoreAsyncSample
{
    public async Task<long> UpdateUsingPartitionedDmlCoreAsync(string projectId, string instanceId, string databaseId)
    {
        string connectionString = $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}";

        using var connection = new SpannerConnection(connectionString);
        await connection.OpenAsync();

        using var cmd = connection.CreateDmlCommand("UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1");
        long rowCount = await cmd.ExecutePartitionedUpdateAsync();

        Console.WriteLine($"{rowCount} row(s) updated...");
        return rowCount;
    }
}

Go

使用 PartitionedUpdate() 方法来执行分区 DML 语句。


import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/spanner"
)

func updateUsingPartitionedDML(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	stmt := spanner.Statement{SQL: "UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1"}
	rowCount, err := client.PartitionedUpdate(ctx, stmt)
	if err != nil {
		return err
	}
	fmt.Fprintf(w, "%d record(s) updated.\n", rowCount)
	return nil
}

Java

使用 executePartitionedUpdate() 方法来执行分区 DML 语句。

static void updateUsingPartitionedDml(DatabaseClient dbClient) {
  String sql = "UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1";
  long rowCount = dbClient.executePartitionedUpdate(Statement.of(sql));
  System.out.printf("%d records updated.\n", rowCount);
}

Node.js

使用 runPartitionedUpdate() 方法来执行分区 DML 语句。

// Imports the Google Cloud client library
const {Spanner} = require('@google-cloud/spanner');

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// const projectId = 'my-project-id';
// const instanceId = 'my-instance';
// const databaseId = 'my-database';

// Creates a client
const spanner = new Spanner({
  projectId: projectId,
});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

try {
  const [rowCount] = await database.runPartitionedUpdate({
    sql: 'UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1',
  });
  console.log(`Successfully updated ${rowCount} records.`);
} catch (err) {
  console.error('ERROR:', err);
} finally {
  // Close the database when finished.
  database.close();
}

PHP

使用 executePartitionedUpdate() 方法来执行分区 DML 语句。

use Google\Cloud\Spanner\SpannerClient;

/**
 * Updates sample data in the database by partition with a DML statement.
 *
 * This updates the `MarketingBudget` column which must be created before
 * running this sample. You can add the column by running the `add_column`
 * sample or by running this DDL statement against your database:
 *
 *     ALTER TABLE Albums ADD COLUMN MarketingBudget INT64
 *
 * Example:
 * ```
 * update_data($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function update_data_with_partitioned_dml(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $rowCount = $database->executePartitionedUpdate(
        'UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1'
    );

    printf('Updated %d row(s).' . PHP_EOL, $rowCount);
}

Python

使用 execute_partitioned_dml() 方法来执行分区 DML 语句。

# instance_id = "your-spanner-instance"
# database_id = "your-spanner-db-id"

spanner_client = spanner.Client()
instance = spanner_client.instance(instance_id)
database = instance.database(database_id)

row_ct = database.execute_partitioned_dml(
    "UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1"
)

print("{} records updated.".format(row_ct))

Ruby

使用 execute_partitioned_update() 方法来执行分区 DML 语句。

# project_id  = "Your Google Cloud project ID"
# instance_id = "Your Spanner instance ID"
# database_id = "Your Spanner database ID"

require "google/cloud/spanner"

spanner = Google::Cloud::Spanner.new project: project_id
client  = spanner.client instance_id, database_id

row_count = client.execute_partition_update(
  "UPDATE Albums SET MarketingBudget = 100000 WHERE SingerId > 1"
)

puts "#{row_count} records updated."

以下代码示例根据 SingerId 列从 Singers 表中删除行。

C++

void DmlPartitionedDelete(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;
  auto result = client.ExecutePartitionedDml(
      spanner::SqlStatement("DELETE FROM Singers WHERE SingerId > 10"));
  if (!result) throw std::move(result).status();
  std::cout << "Deleted at least " << result->row_count_lower_bound
            << " row(s) [spanner_dml_partitioned_delete]\n";
}

C#


using Google.Cloud.Spanner.Data;
using System;
using System.Threading.Tasks;

public class DeleteUsingPartitionedDmlCoreAsyncSample
{
    public async Task<long> DeleteUsingPartitionedDmlCoreAsync(string projectId, string instanceId, string databaseId)
    {
        string connectionString = $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}";

        using var connection = new SpannerConnection(connectionString);
        await connection.OpenAsync();

        using var cmd = connection.CreateDmlCommand("DELETE FROM Singers WHERE SingerId > 10");
        long rowCount = await cmd.ExecutePartitionedUpdateAsync();

        Console.WriteLine($"{rowCount} row(s) deleted...");
        return rowCount;
    }
}

Go


import (
	"context"
	"fmt"
	"io"

	"cloud.google.com/go/spanner"
)

func deleteUsingPartitionedDML(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	stmt := spanner.Statement{SQL: "DELETE FROM Singers WHERE SingerId > 10"}
	rowCount, err := client.PartitionedUpdate(ctx, stmt)
	if err != nil {
		return err

	}
	fmt.Fprintf(w, "%d record(s) deleted.", rowCount)
	return nil
}

Java

static void deleteUsingPartitionedDml(DatabaseClient dbClient) {
  String sql = "DELETE FROM Singers WHERE SingerId > 10";
  long rowCount = dbClient.executePartitionedUpdate(Statement.of(sql));
  System.out.printf("%d records deleted.\n", rowCount);
}

Node.js

// Imports the Google Cloud client library
const {Spanner} = require('@google-cloud/spanner');

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// const projectId = 'my-project-id';
// const instanceId = 'my-instance';
// const databaseId = 'my-database';

// Creates a client
const spanner = new Spanner({
  projectId: projectId,
});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

try {
  const [rowCount] = await database.runPartitionedUpdate({
    sql: 'DELETE FROM Singers WHERE SingerId > 10',
  });
  console.log(`Successfully deleted ${rowCount} records.`);
} catch (err) {
  console.error('ERROR:', err);
} finally {
  // Close the database when finished.
  database.close();
}

PHP

use Google\Cloud\Spanner\SpannerClient;

/**
 * Delete sample data in the database by partition with a DML statement.
 *
 * This updates the `MarketingBudget` column which must be created before
 * running this sample. You can add the column by running the `add_column`
 * sample or by running this DDL statement against your database:
 *
 *     ALTER TABLE Albums ADD COLUMN MarketingBudget INT64
 *
 * Example:
 * ```
 * update_data($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function delete_data_with_partitioned_dml(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $rowCount = $database->executePartitionedUpdate(
        'DELETE FROM Singers WHERE SingerId > 10'
    );

    printf('Deleted %d row(s).' . PHP_EOL, $rowCount);
}

Python

# instance_id = "your-spanner-instance"
# database_id = "your-spanner-db-id"
spanner_client = spanner.Client()
instance = spanner_client.instance(instance_id)
database = instance.database(database_id)

row_ct = database.execute_partitioned_dml("DELETE FROM Singers WHERE SingerId > 10")

print("{} record(s) deleted.".format(row_ct))

Ruby

# project_id  = "Your Google Cloud project ID"
# instance_id = "Your Spanner instance ID"
# database_id = "Your Spanner database ID"

require "google/cloud/spanner"

spanner = Google::Cloud::Spanner.new project: project_id
client  = spanner.client instance_id, database_id

row_count = client.execute_partition_update(
  "DELETE FROM Singers WHERE SingerId > 10"
)

puts "#{row_count} records deleted."