components::Postgres Class Reference

Table of Contents

• Public Member Functions
• Static Public Member Functions
• Static Public Attributes
• Detailed Description
• Dynamic options:
• Static configuration example:
• Secdist format
• Predefined roles
• Automatic discovery
• Static options:
• Member Function Documentation
• GetDatabase()
• Member Data Documentation
• kDefaultCommandControl
• kDefaultMaxReplicationLag
• kDefaultShardNumber

PosgreSQL client component. More...

#include <userver/storages/postgres/component.hpp>

Inheritance diagram for components::Postgres:

Collaboration diagram for components::Postgres:

Public Member Functions
	Postgres (const ComponentConfig &, const ComponentContext &)
	Component constructor.
	~Postgres () override
	Component destructor.
storages::postgres::ClusterPtr	GetCluster () const
	Cluster accessor for default shard number.
storages::postgres::ClusterPtr	GetClusterForShard (size_t shard) const
	Cluster accessor for specific shard number.
size_t	GetShardCount () const
	Get total shard count.
storages::postgres::DatabasePtr	GetDatabase () const
	Get database object.
void	ExtendStatistics (utils::statistics::Writer &writer)
	Reports statistics for PostgreSQL driver.
Public Member Functions inherited from components::LoggableComponentBase
	LoggableComponentBase (const ComponentConfig &, const ComponentContext &)
	LoggableComponentBase (LoggableComponentBase &&)=delete
	LoggableComponentBase (const LoggableComponentBase &)=delete
	~LoggableComponentBase () override=default
ComponentHealth	GetComponentHealth () const override
void	OnLoadingCancelled () override
void	OnAllComponentsLoaded () override
void	OnAllComponentsAreStopping () override

Static Public Member Functions
static yaml_config::Schema	GetStaticConfigSchema ()
Static Public Member Functions inherited from components::LoggableComponentBase
static yaml_config::Schema	GetStaticConfigSchema ()

Static Public Attributes
static constexpr auto	kDefaultMaxReplicationLag = std::chrono::seconds{60}
static constexpr size_t	kDefaultShardNumber = 0
	Default shard number.
static constexpr storages::postgres::CommandControl	kDefaultCommandControl
	Default command control.

Detailed Description

PosgreSQL client component.

Provides access to a PostgreSQL cluster.

Dynamic options:

• POSTGRES_DEFAULT_COMMAND_CONTROL
• POSTGRES_HANDLERS_COMMAND_CONTROL
• POSTGRES_QUERIES_COMMAND_CONTROL
• POSTGRES_CONNECTION_POOL_SETTINGS
• POSTGRES_CONNECTION_SETTINGS
• POSTGRES_STATEMENT_METRICS_SETTINGS
• POSTGRES_CONNLIMIT_MODE_AUTO_ENABLED

Static configuration example:

postgres-taxi:
  dbalias: taxi
  blocking_task_processor: task-processor-name
  max_replication_lag: 60s
  min_pool_size: 4
  max_pool_size: 15
  max_queue_size: 200
  max_statement_metrics: 50

You must specify either dbalias or conn_info. If the component is configured with an alias, it will lookup connection data in secdist.json

You must specify blocking_task_processor as well.

max_replication_lag can be used to tune replication lag limit for replicas. Once the replica lag exceeds this value it will be automatically disabled. Note, however, that client-size lag detection is not precise in nature and can only provide the precision of couple seconds.

Secdist format

A PosgreSQL alias in secdist is described as a JSON array of objects containing a single cluster description. There are two formats of describing a cluster, the first one assigns predefined roles to DSNs, the second one is just a list of DSNs and the Postgres component takes care of discovering the cluster's topology itself.

Predefined roles

In predefined roles format the component requires single-host connection strings.

{
  "shard_number" : 0,
  "master": "host=localhost dbname=example",
  "sync_slave": "host=localhost dbname=example",
  "slaves": [
    "host=localhost dbname=example"
  ]
}

The predefined roles format is deprecated and the support will be removed soon.

Automatic discovery

In automatic discovery format the connection strings are any valid PostgreSQL connection strings including multi-host ones with the exception of target_session_attrs which will be ignored.

{
  "shard_number" : 0,
  "hosts": [
    "host=host1,host2,host3 dbname=example",
    "postgresql://host1:5432,host2:6432,host3:12000/example"
  ]
}

The shard_number parameter is required in both formats and must match the index of cluster description object in the alias array.

Please see PostgreSQL documentation on connection strings.

Static options:

Name	Description	Default value
dbalias	name of the database in secdist config (if available)	–
dbconnection	connection DSN string (used if no dbalias specified)	–
blocking_task_processor	name of task processor for background blocking operations	–
max_replication_lag	replication lag limit for usable slaves	60s
min_pool_size	number of connections created initially	4
max_pool_size	limit of connections count	15
sync-start	perform initial connections synchronously	false
dns_resolver	server hostname resolver type (getaddrinfo or async)	'async'
persistent-prepared-statements	cache prepared statements or not	true
user-types-enabled	disabling will disallow use of user-defined types	true
ignore_unused_query_params	disable check for not-NULL query params that are not used in query	false
monitoring-dbalias	name of the database for monitorings	calculated from dbalias or dbconnection options
max_prepared_cache_size	prepared statements cache size limit	5000
max_statement_metrics	limit of exported metrics for named statements	0
min_pool_size	number of connections created initially	4
max_pool_size	maximum number of created connections	15
max_queue_size	maximum number of clients waiting for a connection	200
connecting_limit	limit for concurrent establishing connections number per pool (0 - unlimited)	0
connlimit_mode	max_connections setup mode (manual or auto)	auto
error-injection	artificial error injection settings, error_injection::Settings	–

Examples

postgresql/functional_tests/basic_chaos/postgres_service.cpp, and samples/digest_auth_service/auth_digest.cpp.

Definition at line 137 of file component.hpp.

Member Function Documentation

GetDatabase()

storages::postgres::DatabasePtr components::Postgres::GetDatabase ( ) const

inline

Get database object.

Definition at line 163 of file component.hpp.

Member Data Documentation

kDefaultCommandControl

constexpr storages::postgres::CommandControl components::Postgres::kDefaultCommandControl

staticconstexpr

Initial value:

{
      std::chrono::milliseconds{500},  
      std::chrono::milliseconds{250}   
  }

Default command control.

Definition at line 143 of file component.hpp.

kDefaultMaxReplicationLag

constexpr auto components::Postgres::kDefaultMaxReplicationLag = std::chrono::seconds{60}

staticconstexpr

Definition at line 139 of file component.hpp.

kDefaultShardNumber

constexpr size_t components::Postgres::kDefaultShardNumber = 0

staticconstexpr

Default shard number.

Definition at line 141 of file component.hpp.

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The documentation for this class was generated from the following file:

• userver/storages/postgres/component.hpp