Enumerations

Kind

static

number

The kind of PlanNode. Distinguishes between the two different kinds of nodes that can appear in a query plan.

Value

KIND_UNSPECIFIED

Not specified.

RELATIONAL

Denotes a Relational operator node in the expression tree. Relational operators represent iterative processing of rows during query execution. For example, a TableScan operation that reads rows from a table.

SCALAR

Denotes a Scalar node in the expression tree. Scalar nodes represent non-iterable entities in the query plan. For example, constants or arithmetic operators appearing inside predicate expressions or references to column names.

QueryMode

static

number

Mode in which the query must be processed.

Value

NORMAL

The default mode where only the query result, without any information about the query plan is returned.

PLAN

This mode returns only the query plan, without any result rows or execution statistics information.

PROFILE

This mode returns both the query plan and the execution statistics along with the result rows.

Properties

Kind

static

number

The kind of PlanNode. Distinguishes between the two different kinds of nodes that can appear in a query plan.

Value

KIND_UNSPECIFIED

Not specified.

RELATIONAL

Denotes a Relational operator node in the expression tree. Relational operators represent iterative processing of rows during query execution. For example, a TableScan operation that reads rows from a table.

SCALAR

Denotes a Scalar node in the expression tree. Scalar nodes represent non-iterable entities in the query plan. For example, constants or arithmetic operators appearing inside predicate expressions or references to column names.

QueryMode

static

number

Mode in which the query must be processed.

Value

NORMAL

The default mode where only the query result, without any information about the query plan is returned.

PLAN

This mode returns only the query plan, without any result rows or execution statistics information.

PROFILE

This mode returns both the query plan and the execution statistics along with the result rows.

Abstract types

BeginTransactionRequest

static

The request for BeginTransaction.

Properties

Parameter

session

string

Required. The session in which the transaction runs.

options

Object

Required. Options for the new transaction.

This object should have the same structure as TransactionOptions

See also

google.spanner.v1.BeginTransactionRequest definition in proto format

static

Metadata associated with a parent-child relationship appearing in a PlanNode.

Properties

Parameter

childIndex

number

The node to which the link points.

type

string

The type of the link. For example, in Hash Joins this could be used to distinguish between the build child and the probe child, or in the case of the child being an output variable, to represent the tag associated with the output variable.

variable

string

Only present if the child node is SCALAR and corresponds to an output variable of the parent node. The field carries the name of the output variable. For example, a TableScan operator that reads rows from a table will have child links to the SCALAR nodes representing the output variables created for each column that is read by the operator. The corresponding variable fields will be set to the variable names assigned to the columns.

See also

google.spanner.v1.PlanNode.ChildLink definition in proto format

CommitRequest

static

The request for Commit.

Properties

Parameter

session

string

Required. The session in which the transaction to be committed is running.

transactionId

string

Commit a previously-started transaction.

singleUseTransaction

Object

Execute mutations in a temporary transaction. Note that unlike commit of a previously-started transaction, commit with a temporary transaction is non-idempotent. That is, if the CommitRequest is sent to Cloud Spanner more than once (for instance, due to retries in the application, or in the transport library), it is possible that the mutations are executed more than once. If this is undesirable, use BeginTransaction and Commit instead.

This object should have the same structure as TransactionOptions

mutations

Array of Object

The mutations to be executed when this transaction commits. All mutations are applied atomically, in the order they appear in this list.

This object should have the same structure as Mutation

See also

google.spanner.v1.CommitRequest definition in proto format

CommitResponse

static

The response for Commit.

Property

Parameter

commitTimestamp

Object

The Cloud Spanner timestamp at which the transaction committed.

This object should have the same structure as Timestamp

See also

google.spanner.v1.CommitResponse definition in proto format

CreateSessionRequest

static

The request for CreateSession.

Properties

Parameter

database

string

Required. The database in which the new session is created.

session

Object

The session to create.

This object should have the same structure as Session

See also

google.spanner.v1.CreateSessionRequest definition in proto format

Delete

static

Arguments to delete operations.

Properties

Parameter

table

string

Required. The table whose rows will be deleted.

keySet

Object

Required. The primary keys of the rows within table to delete.

This object should have the same structure as KeySet

See also

google.spanner.v1.Mutation.Delete definition in proto format

DeleteSessionRequest

static

The request for DeleteSession.

Property

Parameter

name

string

Required. The name of the session to delete.

See also

google.spanner.v1.DeleteSessionRequest definition in proto format

ExecuteSqlRequest

static

The request for ExecuteSql and ExecuteStreamingSql.

Properties

Parameter

session

string

Required. The session in which the SQL query should be performed.

transaction

Object

The transaction to use. If none is provided, the default is a temporary read-only transaction with strong concurrency.

This object should have the same structure as TransactionSelector

sql

string

Required. The SQL query string.

params

Object

The SQL query string can contain parameter placeholders. A parameter placeholder consists of '@' followed by the parameter name. Parameter names consist of any combination of letters, numbers, and underscores.

Parameters can appear anywhere that a literal value is expected. The same parameter name can be used more than once, for example: "WHERE id > @msg_id AND id < @msg_id + 100"

It is an error to execute an SQL query with unbound parameters.

Parameter values are specified using params, which is a JSON object whose keys are parameter names, and whose values are the corresponding parameter values.

This object should have the same structure as Struct

paramTypes

Object with Object properties

It is not always possible for Cloud Spanner to infer the right SQL type from a JSON value. For example, values of type BYTES and values of type STRING both appear in params as JSON strings.

In these cases, param_types can be used to specify the exact SQL type for some or all of the SQL query parameters. See the definition of Type for more information about SQL types.

resumeToken

string

If this request is resuming a previously interrupted SQL query execution, resume_token should be copied from the last PartialResultSet yielded before the interruption. Doing this enables the new SQL query execution to resume where the last one left off. The rest of the request parameters must exactly match the request that yielded this token.

queryMode

number

Used to control the amount of debugging information returned in ResultSetStats.

The number should be among the values of QueryMode

See also

google.spanner.v1.ExecuteSqlRequest definition in proto format

GetSessionRequest

static

The request for GetSession.

Property

Parameter

name

string

Required. The name of the session to retrieve.

See also

google.spanner.v1.GetSessionRequest definition in proto format

KeyRange

static

KeyRange represents a range of rows in a table or index.

A range has a start key and an end key. These keys can be open or closed, indicating if the range includes rows with that key.

Keys are represented by lists, where the ith value in the list corresponds to the ith component of the table or index primary key. Individual values are encoded as described here.

For example, consider the following table definition:

CREATE TABLE UserEvents (
  UserName STRING(MAX),
  EventDate STRING(10)
) PRIMARY KEY(UserName, EventDate);

The following keys name rows in this table:

["Bob", "2014-09-23"]
["Alfred", "2015-06-12"]

Since the UserEvents table's PRIMARY KEY clause names two columns, each UserEvents key has two elements; the first is the UserName, and the second is the EventDate.

Key ranges with multiple components are interpreted lexicographically by component using the table or index key's declared sort order. For example, the following range returns all events for user "Bob" that occurred in the year 2015:

"start_closed": ["Bob", "2015-01-01"]
"end_closed": ["Bob", "2015-12-31"]

Start and end keys can omit trailing key components. This affects the inclusion and exclusion of rows that exactly match the provided key components: if the key is closed, then rows that exactly match the provided components are included; if the key is open, then rows that exactly match are not included.

For example, the following range includes all events for "Bob" that occurred during and after the year 2000:

"start_closed": ["Bob", "2000-01-01"]
"end_closed": ["Bob"]

The next example retrieves all events for "Bob":

"start_closed": ["Bob"]
"end_closed": ["Bob"]

To retrieve events before the year 2000:

"start_closed": ["Bob"]
"end_open": ["Bob", "2000-01-01"]

The following range includes all rows in the table:

"start_closed": []
"end_closed": []

This range returns all users whose UserName begins with any character from A to C:

"start_closed": ["A"]
"end_open": ["D"]

This range returns all users whose UserName begins with B:

"start_closed": ["B"]
"end_open": ["C"]

Key ranges honor column sort order. For example, suppose a table is defined as follows:

CREATE TABLE DescendingSortedTable {
  Key INT64,
  ...
) PRIMARY KEY(Key DESC);

The following range retrieves all rows with key values between 1 and 100 inclusive:

"start_closed": ["100"]
"end_closed": ["1"]

Note that 100 is passed as the start, and 1 is passed as the end, because Key is a descending column in the schema.

Properties

Parameter

startClosed

Object

If the start is closed, then the range includes all rows whose first len(start_closed) key columns exactly match start_closed.

This object should have the same structure as ListValue

startOpen

Object

If the start is open, then the range excludes rows whose first len(start_open) key columns exactly match start_open.

This object should have the same structure as ListValue

endClosed

Object

If the end is closed, then the range includes all rows whose first len(end_closed) key columns exactly match end_closed.

This object should have the same structure as ListValue

endOpen

Object

If the end is open, then the range excludes rows whose first len(end_open) key columns exactly match end_open.

This object should have the same structure as ListValue

See also

google.spanner.v1.KeyRange definition in proto format

KeySet

static

KeySet defines a collection of Cloud Spanner keys and/or key ranges. All the keys are expected to be in the same table or index. The keys need not be sorted in any particular way.

If the same key is specified multiple times in the set (for example if two ranges, two keys, or a key and a range overlap), Cloud Spanner behaves as if the key were only specified once.

Properties

Parameter

keys

Array of Object

A list of specific keys. Entries in keys should have exactly as many elements as there are columns in the primary or index key with which this KeySet is used. Individual key values are encoded as described here.

This object should have the same structure as ListValue

ranges

Array of Object

A list of key ranges. See KeyRange for more information about key range specifications.

This object should have the same structure as KeyRange

all

boolean

For convenience all can be set to true to indicate that this KeySet matches all keys in the table or index. Note that any keys specified in keys or ranges are only yielded once.

See also

google.spanner.v1.KeySet definition in proto format

ListSessionsRequest

static

The request for ListSessions.

Properties

Parameter

database

string

Required. The database in which to list sessions.

pageSize

number

Number of sessions to be returned in the response. If 0 or less, defaults to the server's maximum allowed page size.

pageToken

string

If non-empty, page_token should contain a next_page_token from a previous ListSessionsResponse.

filter

string

An expression for filtering the results of the request. Filter rules are case insensitive. The fields eligible for filtering are:

* `labels.key` where key is the name of a label

Some examples of using filters are:

* `labels.env:*` --> The session has the label "env".
* `labels.env:dev` --> The session has the label "env" and the value of
                     the label contains the string "dev".
See also

google.spanner.v1.ListSessionsRequest definition in proto format

ListSessionsResponse

static

The response for ListSessions.

Properties

Parameter

sessions

Array of Object

The list of requested sessions.

This object should have the same structure as Session

nextPageToken

string

next_page_token can be sent in a subsequent ListSessions call to fetch more of the matching sessions.

See also

google.spanner.v1.ListSessionsResponse definition in proto format

Mutation

static

A modification to one or more Cloud Spanner rows. Mutations can be applied to a Cloud Spanner database by sending them in a Commit call.

Properties

Parameter

insert

Object

Insert new rows in a table. If any of the rows already exist, the write or transaction fails with error ALREADY_EXISTS.

This object should have the same structure as Write

update

Object

Update existing rows in a table. If any of the rows does not already exist, the transaction fails with error NOT_FOUND.

This object should have the same structure as Write

insertOrUpdate

Object

Like insert, except that if the row already exists, then its column values are overwritten with the ones provided. Any column values not explicitly written are preserved.

This object should have the same structure as Write

replace

Object

Like insert, except that if the row already exists, it is deleted, and the column values provided are inserted instead. Unlike insert_or_update, this means any values not explicitly written become NULL.

This object should have the same structure as Write

delete

Object

Delete rows from a table. Succeeds whether or not the named rows were present.

This object should have the same structure as Delete

See also

google.spanner.v1.Mutation definition in proto format

PartialResultSet

static

Partial results from a streaming read or SQL query. Streaming reads and SQL queries better tolerate large result sets, large rows, and large values, but are a little trickier to consume.

Properties

Parameter

metadata

Object

Metadata about the result set, such as row type information. Only present in the first response.

This object should have the same structure as ResultSetMetadata

values

Array of Object

A streamed result set consists of a stream of values, which might be split into many PartialResultSet messages to accommodate large rows and/or large values. Every N complete values defines a row, where N is equal to the number of entries in metadata.row_type.fields.

Most values are encoded based on type as described here.

It is possible that the last value in values is "chunked", meaning that the rest of the value is sent in subsequent PartialResultSet(s). This is denoted by the chunked_value field. Two or more chunked values can be merged to form a complete value as follows:

 bool/number/null: cannot be chunked
 string: concatenate the strings
 list: concatenate the lists. If the last element in a list is a
  string, list, or object, merge it with the first element in
  the next list by applying these rules recursively.
 object: concatenate the (field name, field value) pairs. If a
  field name is duplicated, then apply these rules recursively
  to merge the field values.

Some examples of merging:

  # Strings are concatenated.
  "foo", "bar" => "foobar"

  # Lists of non-strings are concatenated.
  [2, 3], [4] => [2, 3, 4]

  # Lists are concatenated, but the last and first elements are merged
  # because they are strings.
  ["a", "b"], ["c", "d"] => ["a", "bc", "d"]

  # Lists are concatenated, but the last and first elements are merged
  # because they are lists. Recursively, the last and first elements
  # of the inner lists are merged because they are strings.
  ["a", ["b", "c"]], [["d"], "e"] => ["a", ["b", "cd"], "e"]

  # Non-overlapping object fields are combined.
  {"a": "1"}, {"b": "2"} => {"a": "1", "b": 2"}

  # Overlapping object fields are merged.
  {"a": "1"}, {"a": "2"} => {"a": "12"}

  # Examples of merging objects containing lists of strings.
  {"a": ["1"]}, {"a": ["2"]} => {"a": ["12"]}

For a more complete example, suppose a streaming SQL query is yielding a result set whose rows contain a single string field. The following PartialResultSets might be yielded:

  {
    "metadata": { ... }
    "values": ["Hello", "W"]
    "chunked_value": true
    "resume_token": "Af65..."
  }
  {
    "values": ["orl"]
    "chunked_value": true
    "resume_token": "Bqp2..."
  }
  {
    "values": ["d"]
    "resume_token": "Zx1B..."
  }

This sequence of PartialResultSets encodes two rows, one containing the field value "Hello", and a second containing the field value "World" = "W" + "orl" + "d".

This object should have the same structure as Value

chunkedValue

boolean

If true, then the final value in values is chunked, and must be combined with more values from subsequent PartialResultSets to obtain a complete field value.

resumeToken

string

Streaming calls might be interrupted for a variety of reasons, such as TCP connection loss. If this occurs, the stream of results can be resumed by re-sending the original request and including resume_token. Note that executing any other transaction in the same session invalidates the token.

stats

Object

Query plan and execution statistics for the query that produced this streaming result set. These can be requested by setting ExecuteSqlRequest.query_mode and are sent only once with the last response in the stream.

This object should have the same structure as ResultSetStats

See also

google.spanner.v1.PartialResultSet definition in proto format

PlanNode

static

Node information for nodes appearing in a QueryPlan.plan_nodes.

Properties

Parameter

index

number

The PlanNode's index in node list.

kind

number

Used to determine the type of node. May be needed for visualizing different kinds of nodes differently. For example, If the node is a SCALAR node, it will have a condensed representation which can be used to directly embed a description of the node in its parent.

The number should be among the values of Kind

displayName

string

The display name for the node.

childLinks

Array of Object

List of child node indexes and their relationship to this parent.

This object should have the same structure as ChildLink

shortRepresentation

Object

Condensed representation for SCALAR nodes.

This object should have the same structure as ShortRepresentation

metadata

Object

Attributes relevant to the node contained in a group of key-value pairs. For example, a Parameter Reference node could have the following information in its metadata:

  {
    "parameter_reference": "param1",
    "parameter_type": "array"
  }

This object should have the same structure as Struct

executionStats

Object

The execution statistics associated with the node, contained in a group of key-value pairs. Only present if the plan was returned as a result of a profile query. For example, number of executions, number of rows/time per execution etc.

This object should have the same structure as Struct

See also

google.spanner.v1.PlanNode definition in proto format

QueryPlan

static

Contains an ordered list of nodes appearing in the query plan.

Property

Parameter

planNodes

Array of Object

The nodes in the query plan. Plan nodes are returned in pre-order starting with the plan root. Each PlanNode's id corresponds to its index in plan_nodes.

This object should have the same structure as PlanNode

See also

google.spanner.v1.QueryPlan definition in proto format

ReadOnly

static

Message type to initiate a read-only transaction.

Properties

Parameter

strong

boolean

Read at a timestamp where all previously committed transactions are visible.

minReadTimestamp

Object

Executes all reads at a timestamp >= min_read_timestamp.

This is useful for requesting fresher data than some previous read, or data that is fresh enough to observe the effects of some previously committed transaction whose timestamp is known.

Note that this option can only be used in single-use transactions.

A timestamp in RFC3339 UTC \"Zulu\" format, accurate to nanoseconds. Example: "2014-10-02T15:01:23.045123456Z".

This object should have the same structure as Timestamp

maxStaleness

Object

Read data at a timestamp >= NOW - max_staleness seconds. Guarantees that all writes that have committed more than the specified number of seconds ago are visible. Because Cloud Spanner chooses the exact timestamp, this mode works even if the client's local clock is substantially skewed from Cloud Spanner commit timestamps.

Useful for reading the freshest data available at a nearby replica, while bounding the possible staleness if the local replica has fallen behind.

Note that this option can only be used in single-use transactions.

This object should have the same structure as Duration

readTimestamp

Object

Executes all reads at the given timestamp. Unlike other modes, reads at a specific timestamp are repeatable; the same read at the same timestamp always returns the same data. If the timestamp is in the future, the read will block until the specified timestamp, modulo the read's deadline.

Useful for large scale consistent reads such as mapreduces, or for coordinating many reads against a consistent snapshot of the data.

A timestamp in RFC3339 UTC \"Zulu\" format, accurate to nanoseconds. Example: "2014-10-02T15:01:23.045123456Z".

This object should have the same structure as Timestamp

exactStaleness

Object

Executes all reads at a timestamp that is exact_staleness old. The timestamp is chosen soon after the read is started.

Guarantees that all writes that have committed more than the specified number of seconds ago are visible. Because Cloud Spanner chooses the exact timestamp, this mode works even if the client's local clock is substantially skewed from Cloud Spanner commit timestamps.

Useful for reading at nearby replicas without the distributed timestamp negotiation overhead of max_staleness.

This object should have the same structure as Duration

returnReadTimestamp

boolean

If true, the Cloud Spanner-selected read timestamp is included in the Transaction message that describes the transaction.

See also

google.spanner.v1.TransactionOptions.ReadOnly definition in proto format

ReadRequest

static

The request for Read and StreamingRead.

Properties

Parameter

session

string

Required. The session in which the read should be performed.

transaction

Object

The transaction to use. If none is provided, the default is a temporary read-only transaction with strong concurrency.

This object should have the same structure as TransactionSelector

table

string

Required. The name of the table in the database to be read.

index

string

If non-empty, the name of an index on table. This index is used instead of the table primary key when interpreting key_set and sorting result rows. See key_set for further information.

columns

Array of string

The columns of table to be returned for each row matching this request.

keySet

Object

Required. key_set identifies the rows to be yielded. key_set names the primary keys of the rows in table to be yielded, unless index is present. If index is present, then key_set instead names index keys in index.

Rows are yielded in table primary key order (if index is empty) or index key order (if index is non-empty).

It is not an error for the key_set to name rows that do not exist in the database. Read yields nothing for nonexistent rows.

This object should have the same structure as KeySet

limit

number

If greater than zero, only the first limit rows are yielded. If limit is zero, the default is no limit.

resumeToken

string

If this request is resuming a previously interrupted read, resume_token should be copied from the last PartialResultSet yielded before the interruption. Doing this enables the new read to resume where the last read left off. The rest of the request parameters must exactly match the request that yielded this token.

See also

google.spanner.v1.ReadRequest definition in proto format

ReadWrite

static

Message type to initiate a read-write transaction. Currently this transaction type has no options.

See also

google.spanner.v1.TransactionOptions.ReadWrite definition in proto format

ResultSet

static

Results from Read or ExecuteSql.

Properties

Parameter

metadata

Object

Metadata about the result set, such as row type information.

This object should have the same structure as ResultSetMetadata

rows

Array of Object

Each element in rows is a row whose format is defined by metadata.row_type. The ith element in each row matches the ith field in metadata.row_type. Elements are encoded based on type as described here.

This object should have the same structure as ListValue

stats

Object

Query plan and execution statistics for the query that produced this result set. These can be requested by setting ExecuteSqlRequest.query_mode.

This object should have the same structure as ResultSetStats

See also

google.spanner.v1.ResultSet definition in proto format

ResultSetMetadata

static

Metadata about a ResultSet or PartialResultSet.

Properties

Parameter

rowType

Object

Indicates the field names and types for the rows in the result set. For example, a SQL query like "SELECT UserId, UserName FROM Users" could return a row_type value like:

  "fields": [
    { "name": "UserId", "type": { "code": "INT64" } },
    { "name": "UserName", "type": { "code": "STRING" } },
  ]

This object should have the same structure as StructType

transaction

Object

If the read or SQL query began a transaction as a side-effect, the information about the new transaction is yielded here.

This object should have the same structure as Transaction

See also

google.spanner.v1.ResultSetMetadata definition in proto format

ResultSetStats

static

Additional statistics about a ResultSet or PartialResultSet.

Properties

Parameter

queryPlan

Object

QueryPlan for the query associated with this result.

This object should have the same structure as QueryPlan

queryStats

Object

Aggregated statistics from the execution of the query. Only present when the query is profiled. For example, a query could return the statistics as follows:

  {
    "rows_returned": "3",
    "elapsed_time": "1.22 secs",
    "cpu_time": "1.19 secs"
  }

This object should have the same structure as Struct

See also

google.spanner.v1.ResultSetStats definition in proto format

RollbackRequest

static

The request for Rollback.

Properties

Parameter

session

string

Required. The session in which the transaction to roll back is running.

transactionId

string

Required. The transaction to roll back.

See also

google.spanner.v1.RollbackRequest definition in proto format

Session

static

A session in the Cloud Spanner API.

Properties

Parameter

name

string

The name of the session.

labels

Object with string properties

The labels for the session.

  • Label keys must be between 1 and 63 characters long and must conform to the following regular expression: a-z?.
  • Label values must be between 0 and 63 characters long and must conform to the regular expression (a-z?)?.
  • No more than 64 labels can be associated with a given session.

    See https://goo.gl/xmQnxf for more information on and examples of labels.

createTime

Object

Output only. The timestamp when the session is created.

This object should have the same structure as Timestamp

approximateLastUseTime

Object

Output only. The approximate timestamp when the session is last used. It is typically earlier than the actual last use time.

This object should have the same structure as Timestamp

See also

google.spanner.v1.Session definition in proto format

ShortRepresentation

static

Condensed representation of a node and its subtree. Only present for SCALAR PlanNode(s).

Properties

Parameter

description

string

A string representation of the expression subtree rooted at this node.

subqueries

Object with number properties

A mapping of (subquery variable name) -> (subquery node id) for cases where the description string of this node references a SCALAR subquery contained in the expression subtree rooted at this node. The referenced SCALAR subquery may not necessarily be a direct child of this node.

See also

google.spanner.v1.PlanNode.ShortRepresentation definition in proto format

Transaction

static

A transaction.

Properties

Parameter

id

string

id may be used to identify the transaction in subsequent Read, ExecuteSql, Commit, or Rollback calls.

Single-use read-only transactions do not have IDs, because single-use transactions do not support multiple requests.

readTimestamp

Object

For snapshot read-only transactions, the read timestamp chosen for the transaction. Not returned by default: see TransactionOptions.ReadOnly.return_read_timestamp.

A timestamp in RFC3339 UTC \"Zulu\" format, accurate to nanoseconds. Example: "2014-10-02T15:01:23.045123456Z".

This object should have the same structure as Timestamp

See also

google.spanner.v1.Transaction definition in proto format

TransactionOptions

static

Transactions

Each session can have at most one active transaction at a time. After the active transaction is completed, the session can immediately be re-used for the next transaction. It is not necessary to create a new session for each transaction.

Transaction Modes

Cloud Spanner supports two transaction modes:

  1. Locking read-write. This type of transaction is the only way to write data into Cloud Spanner. These transactions rely on pessimistic locking and, if necessary, two-phase commit. Locking read-write transactions may abort, requiring the application to retry.

  2. Snapshot read-only. This transaction type provides guaranteed consistency across several reads, but does not allow writes. Snapshot read-only transactions can be configured to read at timestamps in the past. Snapshot read-only transactions do not need to be committed.

For transactions that only read, snapshot read-only transactions provide simpler semantics and are almost always faster. In particular, read-only transactions do not take locks, so they do not conflict with read-write transactions. As a consequence of not taking locks, they also do not abort, so retry loops are not needed.

Transactions may only read/write data in a single database. They may, however, read/write data in different tables within that database.

Locking Read-Write Transactions

Locking transactions may be used to atomically read-modify-write data anywhere in a database. This type of transaction is externally consistent.

Clients should attempt to minimize the amount of time a transaction is active. Faster transactions commit with higher probability and cause less contention. Cloud Spanner attempts to keep read locks active as long as the transaction continues to do reads, and the transaction has not been terminated by Commit or Rollback. Long periods of inactivity at the client may cause Cloud Spanner to release a transaction's locks and abort it.

Reads performed within a transaction acquire locks on the data being read. Writes can only be done at commit time, after all reads have been completed. Conceptually, a read-write transaction consists of zero or more reads or SQL queries followed by Commit. At any time before Commit, the client can send a Rollback request to abort the transaction.

Semantics

Cloud Spanner can commit the transaction if all read locks it acquired are still valid at commit time, and it is able to acquire write locks for all writes. Cloud Spanner can abort the transaction for any reason. If a commit attempt returns ABORTED, Cloud Spanner guarantees that the transaction has not modified any user data in Cloud Spanner.

Unless the transaction commits, Cloud Spanner makes no guarantees about how long the transaction's locks were held for. It is an error to use Cloud Spanner locks for any sort of mutual exclusion other than between Cloud Spanner transactions themselves.

Retrying Aborted Transactions

When a transaction aborts, the application can choose to retry the whole transaction again. To maximize the chances of successfully committing the retry, the client should execute the retry in the same session as the original attempt. The original session's lock priority increases with each consecutive abort, meaning that each attempt has a slightly better chance of success than the previous.

Under some circumstances (e.g., many transactions attempting to modify the same row(s)), a transaction can abort many times in a short period before successfully committing. Thus, it is not a good idea to cap the number of retries a transaction can attempt; instead, it is better to limit the total amount of wall time spent retrying.

Idle Transactions

A transaction is considered idle if it has no outstanding reads or SQL queries and has not started a read or SQL query within the last 10 seconds. Idle transactions can be aborted by Cloud Spanner so that they don't hold on to locks indefinitely. In that case, the commit will fail with error ABORTED.

If this behavior is undesirable, periodically executing a simple SQL query in the transaction (e.g., SELECT 1) prevents the transaction from becoming idle.

Snapshot Read-Only Transactions

Snapshot read-only transactions provides a simpler method than locking read-write transactions for doing several consistent reads. However, this type of transaction does not support writes.

Snapshot transactions do not take locks. Instead, they work by choosing a Cloud Spanner timestamp, then executing all reads at that timestamp. Since they do not acquire locks, they do not block concurrent read-write transactions.

Unlike locking read-write transactions, snapshot read-only transactions never abort. They can fail if the chosen read timestamp is garbage collected; however, the default garbage collection policy is generous enough that most applications do not need to worry about this in practice.

Snapshot read-only transactions do not need to call Commit or Rollback (and in fact are not permitted to do so).

To execute a snapshot transaction, the client specifies a timestamp bound, which tells Cloud Spanner how to choose a read timestamp.

The types of timestamp bound are:

  • Strong (the default).
  • Bounded staleness.
  • Exact staleness.

If the Cloud Spanner database to be read is geographically distributed, stale read-only transactions can execute more quickly than strong or read-write transaction, because they are able to execute far from the leader replica.

Each type of timestamp bound is discussed in detail below.

Strong

Strong reads are guaranteed to see the effects of all transactions that have committed before the start of the read. Furthermore, all rows yielded by a single read are consistent with each other -- if any part of the read observes a transaction, all parts of the read see the transaction.

Strong reads are not repeatable: two consecutive strong read-only transactions might return inconsistent results if there are concurrent writes. If consistency across reads is required, the reads should be executed within a transaction or at an exact read timestamp.

See TransactionOptions.ReadOnly.strong.

Exact Staleness

These timestamp bounds execute reads at a user-specified timestamp. Reads at a timestamp are guaranteed to see a consistent prefix of the global transaction history: they observe modifications done by all transactions with a commit timestamp <= the read timestamp, and observe none of the modifications done by transactions with a larger commit timestamp. They will block until all conflicting transactions that may be assigned commit timestamps <= the read timestamp have finished.

The timestamp can either be expressed as an absolute Cloud Spanner commit timestamp or a staleness relative to the current time.

These modes do not require a "negotiation phase" to pick a timestamp. As a result, they execute slightly faster than the equivalent boundedly stale concurrency modes. On the other hand, boundedly stale reads usually return fresher results.

See TransactionOptions.ReadOnly.read_timestamp and TransactionOptions.ReadOnly.exact_staleness.

Bounded Staleness

Bounded staleness modes allow Cloud Spanner to pick the read timestamp, subject to a user-provided staleness bound. Cloud Spanner chooses the newest timestamp within the staleness bound that allows execution of the reads at the closest available replica without blocking.

All rows yielded are consistent with each other -- if any part of the read observes a transaction, all parts of the read see the transaction. Boundedly stale reads are not repeatable: two stale reads, even if they use the same staleness bound, can execute at different timestamps and thus return inconsistent results.

Boundedly stale reads execute in two phases: the first phase negotiates a timestamp among all replicas needed to serve the read. In the second phase, reads are executed at the negotiated timestamp.

As a result of the two phase execution, bounded staleness reads are usually a little slower than comparable exact staleness reads. However, they are typically able to return fresher results, and are more likely to execute at the closest replica.

Because the timestamp negotiation requires up-front knowledge of which rows will be read, it can only be used with single-use read-only transactions.

See TransactionOptions.ReadOnly.max_staleness and TransactionOptions.ReadOnly.min_read_timestamp.

Old Read Timestamps and Garbage Collection

Cloud Spanner continuously garbage collects deleted and overwritten data in the background to reclaim storage space. This process is known as "version GC". By default, version GC reclaims versions after they are one hour old. Because of this, Cloud Spanner cannot perform reads at read timestamps more than one hour in the past. This restriction also applies to in-progress reads and/or SQL queries whose timestamp become too old while executing. Reads and SQL queries with too-old read timestamps fail with the error FAILED_PRECONDITION.

Properties

Parameter

readWrite

Object

Transaction may write.

Authorization to begin a read-write transaction requires spanner.databases.beginOrRollbackReadWriteTransaction permission on the session resource.

This object should have the same structure as ReadWrite

readOnly

Object

Transaction will not write.

Authorization to begin a read-only transaction requires spanner.databases.beginReadOnlyTransaction permission on the session resource.

This object should have the same structure as ReadOnly

See also

google.spanner.v1.TransactionOptions definition in proto format

TransactionSelector

static

This message is used to select the transaction in which a Read or ExecuteSql call runs.

See TransactionOptions for more information about transactions.

Properties

Parameter

singleUse

Object

Execute the read or SQL query in a temporary transaction. This is the most efficient way to execute a transaction that consists of a single SQL query.

This object should have the same structure as TransactionOptions

id

string

Execute the read or SQL query in a previously-started transaction.

begin

Object

Begin a new transaction and execute this read or SQL query in it. The transaction ID of the new transaction is returned in ResultSetMetadata.transaction, which is a Transaction.

This object should have the same structure as TransactionOptions

See also

google.spanner.v1.TransactionSelector definition in proto format

Write

static

Arguments to insert, update, insert_or_update, and replace operations.

Properties

Parameter

table

string

Required. The table whose rows will be written.

columns

Array of string

The names of the columns in table to be written.

The list of columns must contain enough columns to allow Cloud Spanner to derive values for all primary key columns in the row(s) to be modified.

values

Array of Object

The values to be written. values can contain more than one list of values. If it does, then multiple rows are written, one for each entry in values. Each list in values must have exactly as many entries as there are entries in columns above. Sending multiple lists is equivalent to sending multiple Mutations, each containing one values entry and repeating table and columns. Individual values in each list are encoded as described here.

This object should have the same structure as ListValue

See also

google.spanner.v1.Mutation.Write definition in proto format