Processes several queries in FIFO manner, optimized for high throughput. More...

#include <pipeline.hxx>

Inheritance diagram for pqxx::pipeline:

Public Types
using	query_id = long
	Identifying numbers for queries. More...

Public Member Functions
	pipeline (pipeline const &)=delete

pipeline &	operator= (pipeline const &)=delete

	pipeline (transaction_base &t)
	Start a pipeline. More...

	pipeline (transaction_base &t, std::string_view tname)
	Start a pipeline. Assign it a name, for more helpful error messages. More...

	~pipeline () noexcept
	Close the pipeline. More...

query_id	insert (std::string_view)
	Add query to the pipeline. More...

void	complete ()
	Wait for all ongoing or pending operations to complete, and detach. More...

void	flush ()
	Forget all ongoing or pending operations and retrieved results. More...

void	cancel ()
	Cancel ongoing query, if any. More...

bool	is_finished (query_id) const
	Is result for given query available? More...

result	retrieve (query_id qid)
	Retrieve result for given query. More...

std::pair< query_id, result >	retrieve ()
	Retrieve oldest unretrieved result (possibly wait for one). More...

bool	empty () const noexcept

int	retain (int retain_max=2)

void	resume ()
	Resume retained query emission. Harmless when not needed. More...

Public Member Functions inherited from pqxx::transaction_focus
	transaction_focus (transaction_base &t, std::string_view cname, std::string_view oname)

	transaction_focus (transaction_base &t, std::string_view cname, std::string &&oname)

	transaction_focus (transaction_base &t, std::string_view cname)

	transaction_focus ()=delete

	transaction_focus (transaction_focus const &)=delete

transaction_focus &	operator= (transaction_focus const &)=delete

std::string_view	classname () const noexcept
	Class name, for human consumption. More...

std::string_view	name () const noexcept
	Name for this object, if the caller passed one; empty string otherwise. More...

std::string	description () const

	transaction_focus (transaction_focus &&)=delete
	Can't move a transaction_focus. More...

transaction_focus &	operator= (transaction_focus &&)=delete
	Can't move a transaction_focus. More...

Additional Inherited Members
Protected Member Functions inherited from pqxx::transaction_focus
void	register_me ()

void	unregister_me () noexcept

void	reg_pending_error (std::string const &) noexcept

bool	registered () const noexcept

Protected Attributes inherited from pqxx::transaction_focus
transaction_base &	m_trans

Detailed Description

Processes several queries in FIFO manner, optimized for high throughput.

Use a pipeline if you want to keep doing useful work while your queries are executing. Result retrieval is decoupled from execution request; queries "go in at the front" and results "come out the back."

Actually, you can retrieve the results in any order if you want, but it may lead to surprising "time travel" effects if any of the queries fails. In particular, syntax errors in the queries can confuse things and show up too early in the stream of results.

Generally, if any of the queries fails, it will throw an exception at the point where you request its result. But it may happen earlier, especially if you request results out of chronological order.

Warning: While a pipeline is active, you cannot execute queries, open streams, etc. on the same transaction. A transaction can have at most one object of a type derived from pqxx::transaction_focus active on it at a time.

Member Typedef Documentation

◆ query_id

using pqxx::pipeline::query_id = long

Identifying numbers for queries.

Constructor & Destructor Documentation

◆ pipeline() [1/3]

pqxx::pipeline::pipeline ( pipeline const & )

delete

◆ pipeline() [2/3]

pqxx::pipeline::pipeline ( transaction_base & t )

explicit

Start a pipeline.

◆ pipeline() [3/3]

pqxx::pipeline::pipeline	(	transaction_base &	t,
		std::string_view	tname
	)

Start a pipeline. Assign it a name, for more helpful error messages.

◆ ~pipeline()

pqxx::pipeline::~pipeline ( )

noexcept

Close the pipeline.

References cancel(), pqxx::transaction_focus::register_me(), pqxx::transaction_focus::registered(), and pqxx::transaction_focus::unregister_me().

Member Function Documentation

◆ cancel()

void pqxx::pipeline::cancel ( )

Cancel ongoing query, if any.

May cancel any or all of the queries that have been inserted at this point whose results have not yet been retrieved. If the pipeline lives in a backend transaction, that transaction may be left in a nonfunctional state in which it can only be aborted.

Therefore, either use this function in a nontransaction, or abort the transaction after calling it.

References pqxx::transaction_base::conn(), and pqxx::transaction_focus::m_trans.

Referenced by ~pipeline().

◆ complete()

void pqxx::pipeline::complete ( )

Wait for all ongoing or pending operations to complete, and detach.

Detaches from the transaction when done.

This does not produce the queries' results, so it may not report any errors which may have occurred in their execution. To be sure that your statements succeeded, call retrieve() until the pipeline is empty.

◆ empty()

bool pqxx::pipeline::empty ( ) const

noexcept

◆ flush()

void pqxx::pipeline::flush ( )

Forget all ongoing or pending operations and retrieved results.

Queries already sent to the backend may still be completed, depending on implementation and timing.

Any error state (unless caused by an internal error) will also be cleared. This is mostly useful in a nontransaction, since a backend transaction is aborted automatically when an error occurs.

Detaches from the transaction when done.

◆ insert()

pqxx::pipeline::query_id pqxx::pipeline::insert ( std::string_view q )

Add query to the pipeline.

Queries accumulate in the pipeline, which sends them to the backend in a batch separated by semicolons. The queries you insert must not use this trick themselves, or the pipeline will get hopelessly confused!

Returns: Identifier for this query, unique only within this pipeline.

◆ is_finished()

bool pqxx::pipeline::is_finished ( pipeline::query_id q ) const

Is result for given query available?

◆ operator=()

pipeline& pqxx::pipeline::operator= ( pipeline const & )

delete

◆ resume()

void pqxx::pipeline::resume ( )

Resume retained query emission. Harmless when not needed.

References pqxx::check_cast(), pqxx::transaction_base::conn(), pqxx::transaction_base::exec(), pqxx::transaction_focus::m_trans, retrieve(), pqxx::separated_list(), pqxx::text, and pqxx::transaction_focus::unregister_me().

Referenced by retain().

◆ retain()

int pqxx::pipeline::retain ( int retain_max = 2 )

Set maximum number of queries to retain before issuing them to the backend. The pipeline will perform better if multiple queries are issued at once, but retaining queries until the results are needed (as opposed to issuing them to the backend immediately) may negate any performance benefits the pipeline can offer.

Recommended practice is to set this value no higher than the number of queries you intend to insert at a time.

Parameters

retain_max A nonnegative "retention capacity;" passing zero will cause queries to be issued immediately

Returns: Old retention capacity

References resume().

◆ retrieve() [1/2]

result pqxx::pipeline::retrieve ( query_id qid )

Retrieve result for given query.

If the query failed for whatever reason, this will throw an exception. The function will block if the query has not finished yet.

Warning: If results are retrieved out-of-order, i.e. in a different order than the one in which their queries were inserted, errors may "propagate" to subsequent queries.

◆ retrieve() [2/2]

std::pair< pqxx::pipeline::query_id, pqxx::result > pqxx::pipeline::retrieve ( )

Retrieve oldest unretrieved result (possibly wait for one).

Returns: The query's identifier and its result set.

Referenced by resume().

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

pipeline.hxx
pipeline.cxx

Public Types

Public Member Functions

Additional Inherited Members