Struct StatementCache 

pub struct StatementCache { /* private fields */ }

Representation of a cache of Statements.

StatementCache is bound to one Client, and Statements generated by that Client must not be used with other Clients.

Preparing the same statement from several tasks at once is coalesced: one of them sends a PREPARE to the database while the others wait for its result, so a burst of concurrent requests for an uncached statement costs a single round trip rather than one per task. If that preparation fails or its task is cancelled, one of the waiting tasks starts a fresh one instead of failing along with it, and nothing is cached until a preparation succeeds.

It can be used like that:

let client = pool.get().await?;
let stmt = client
    .statement_cache
    .prepare(&client, "SELECT 1")
    .await;
let rows = client.query(stmt, &[]).await?;
...

Normally, you probably want to use the ClientWrapper::prepare_cached() and ClientWrapper::prepare_typed_cached() methods instead (or the similar ones on Transaction).

Implementations

impl StatementCache

pub fn size(&self) -> usize

Returns current size of this StatementCache.

pub fn clear(&self)

Clears this StatementCache.

Important: This only clears the StatementCache of one Client instance. If you want to clear the StatementCache of all Clients you should be calling pool.manager().statement_caches.clear() instead.

pub fn remove(&self, query: &str, types: &[Type]) -> Option<Statement>

Removes a Statement from this StatementCache.

Important: This only removes a Statement from one Client cache. If you want to remove a Statement from all StatementCaches you should be calling pool.manager().statement_caches.remove() instead.

pub async fn prepare( &self, client: &PgClient, query: &str, ) -> Result<Statement, Error>

Creates a new prepared Statement using this StatementCache, if possible.

See tokio_postgres::Client::prepare().

pub async fn prepare_typed( &self, client: &PgClient, query: &str, types: &[Type], ) -> Result<Statement, Error>

Creates a new prepared Statement with specifying its Types explicitly using this StatementCache, if possible.

See tokio_postgres::Client::prepare_typed().

Trait Implementations

impl Debug for StatementCache

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.