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6768a71c86
## Problem For #11992 I realised we need to get the type info before executing the query. This is important to know how to decode rows with custom types, eg the following query: ```sql CREATE TYPE foo AS ENUM ('foo','bar','baz'); SELECT ARRAY['foo'::foo, 'bar'::foo, 'baz'::foo] AS data; ``` Getting that to work was harder that it seems. The original tokio-postgres setup has a split between `Client` and `Connection`, where messages are passed between. Because multiple clients were supported, each client message included a dedicated response channel. Each request would be terminated by the `ReadyForQuery` message. The flow I opted to use for parsing types early would not trigger a `ReadyForQuery`. The flow is as follows: ``` PARSE "" // parse the user provided query DESCRIBE "" // describe the query, returning param/result type oids FLUSH // force postgres to flush the responses early // wait for descriptions // check if we know the types, if we don't then // setup the typeinfo query and execute it against each OID: PARSE typeinfo // prepare our typeinfo query DESCRIBE typeinfo FLUSH // force postgres to flush the responses early // wait for typeinfo statement // for each OID we don't know: BIND typeinfo EXECUTE FLUSH // wait for type info, might reveal more OIDs to inspect // close the typeinfo query, we cache the OID->type map and this is kinder to pgbouncer. CLOSE typeinfo // finally once we know all the OIDs: BIND "" // bind the user provided query - already parsed - to the user provided params EXECUTE // run the user provided query SYNC // commit the transaction ``` ## Summary of changes Please review commit by commit. The main challenge was allowing one query to issue multiple sub-queries. To do this I first made sure that the client could fully own the connection, which required removing any shared client state. I then had to replace the way responses are sent to the client, by using only a single permanent channel. This required some additional effort to track which query is being processed. Lastly I had to modify the query/typeinfo functions to not issue `sync` commands, so it would fit into the desired flow above. To note: the flow above does force an extra roundtrip into each query. I don't know yet if this has a measurable latency overhead.
74 lines
2.1 KiB
Rust
74 lines
2.1 KiB
Rust
use crate::query::RowStream;
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use crate::{CancelToken, Client, Error, ReadyForQueryStatus};
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/// A representation of a PostgreSQL database transaction.
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///
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/// Transactions will implicitly roll back when dropped. Use the `commit` method to commit the changes made in the
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/// transaction. Transactions can be nested, with inner transactions implemented via safepoints.
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pub struct Transaction<'a> {
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client: &'a mut Client,
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done: bool,
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}
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impl Drop for Transaction<'_> {
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fn drop(&mut self) {
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if self.done {
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return;
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}
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let _ = self.client.inner_mut().send_simple_query("ROLLBACK");
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}
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}
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impl<'a> Transaction<'a> {
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pub(crate) fn new(client: &'a mut Client) -> Transaction<'a> {
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Transaction {
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client,
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done: false,
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}
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}
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/// Consumes the transaction, committing all changes made within it.
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pub async fn commit(mut self) -> Result<ReadyForQueryStatus, Error> {
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self.done = true;
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self.client.batch_execute("COMMIT").await
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}
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/// Rolls the transaction back, discarding all changes made within it.
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///
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/// This is equivalent to `Transaction`'s `Drop` implementation, but provides any error encountered to the caller.
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pub async fn rollback(mut self) -> Result<ReadyForQueryStatus, Error> {
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self.done = true;
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self.client.batch_execute("ROLLBACK").await
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}
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/// Like `Client::query_raw_txt`.
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pub async fn query_raw_txt<S, I>(
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&mut self,
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statement: &str,
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params: I,
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) -> Result<RowStream, Error>
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where
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S: AsRef<str>,
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I: IntoIterator<Item = Option<S>>,
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I::IntoIter: ExactSizeIterator,
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{
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self.client.query_raw_txt(statement, params).await
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}
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/// Like `Client::cancel_token`.
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pub fn cancel_token(&self) -> CancelToken {
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self.client.cancel_token()
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}
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/// Returns a reference to the underlying `Client`.
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pub fn client(&self) -> &Client {
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self.client
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}
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/// Returns a reference to the underlying `Client`.
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pub fn client_mut(&mut self) -> &mut Client {
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self.client
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}
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}
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