pqxx::pipeline Class Reference

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

#include <pipeline.hxx>

Inheritance diagram for pqxx::pipeline:

List of all members.

Public Types
typedef long	query_id
Public Member Functions
	pipeline (transaction_base &, const PGSTD::string &PName="")
	~pipeline () throw ()
query_id	insert (const PGSTD::string &)
	Add query to the pipeline.
void	complete ()
	Wait for all ongoing or pending operations to complete.
void	flush ()
	Forget all ongoing or pending operations and retrieved results.
bool	is_finished (query_id) const
	Is result for given query available?
result	retrieve (query_id qid)
	Retrieve result for given query.
PGSTD::pair< query_id, result >	retrieve ()
	Retrieve oldest unretrieved result (possibly wait for one).
bool	empty () const throw ()
int	retain (int retain_max=2)
	Set maximum number of queries to retain before issuing them to the backend.
void	resume ()
	Resume retained query emission (harmless when not needed).

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Detailed Description

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

Warning:

This is a prototype, and it may still change radically before becoming a stable part of the library. Also, the class may be very sensitive to exceptions; in certain cases, exceptions occurring in the class may leave a pipeline in a poorly defined state.

Use a pipeline if you want to execute several queries in succession, in situations where some of the queries do not depend on the outcome of the preceding one. Result retrieval is decoupled from execution request; queries "go in at the front" and results "come out the back." In fact, results may be retrieved in any order--though this will be slower than sticking to the order in which they were entered.

Feel free to pump as many queries into the pipeline as possible, even if they were generated after looking at a result from the same pipeline. To get the best possible throughput, try to make insertion of queries run as far ahead of results retrieval as possible; issue each query as early as possible and retrieve their results as late as possible, so the pipeline has as many ongoing queries as possible at any given time. In other words, keep it busy!

One warning: if any of the queries you insert leads to a syntactic error, the error may be returned as if it were generated by an older query. Future versions may try to work around this if working in a nontransaction.

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Member Typedef Documentation

typedef long pqxx::pipeline::query_id

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Constructor & Destructor Documentation

pqxx::pipeline::pipeline (  transaction_base &  , const PGSTD::string &  PName = "" )  [explicit]

pqxx::pipeline::~pipeline (   )  throw ()

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Member Function Documentation

void pqxx::pipeline::complete (   )

Wait for all ongoing or pending operations to complete.

bool pqxx::pipeline::empty (   )  const throw ()

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.

pipeline::query_id pqxx::pipeline::insert (  const PGSTD::string &   )

Add query to the pipeline. Queries are accumulated in the pipeline and sent to the backend in a concatenated format, separated by semicolons. The queries you insert must not use this construct themselves, or the pipeline will get hopelessly confused! Returns: Identifier for this query, unique only within this pipeline

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

Is result for given query available?

void pqxx::pipeline::resume (   )

Resume retained query emission (harmless when not needed).

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

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

Retrieve oldest unretrieved result (possibly wait for one). Returns: The query's identifier and its result set

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.

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

• pipeline.hxx
• pipeline.cxx

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