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Allow synchronous snapshot on replicas and in RDS/Aurora #235

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Allow synchronous snapshot on replicas and in RDS/Aurora #235

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9e1c7eb
Allow synchronous snapshot on replicas and in RDS/Aurora
bdavisab May 31, 2024
c8debc4
Merge branch 'duckdb:main' into allow-sync-snapshot-on-replicas
bdavisab Dec 18, 2024
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29 changes: 5 additions & 24 deletions src/postgres_scanner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -62,40 +62,21 @@ struct PostgresGlobalState : public GlobalTableFunctionState {
PostgresConnection connection;
};

static void PostgresGetSnapshot(PostgresVersion version, const PostgresBindData &bind_data,
PostgresGlobalState &gstate) {
static void PostgresGetSnapshot(const PostgresBindData &bind_data, PostgresGlobalState &gstate) {
unique_ptr<PostgresResult> result;
// by default disable snapshotting
gstate.snapshot = string();
if (gstate.max_threads <= 1) {
return;
}
if (version.type_v == PostgresInstanceType::AURORA) {
return;
}

// reader threads can use the same snapshot
auto &con = gstate.GetConnection();
// pg_stat_wal_receiver was introduced in PostgreSQL 9.6
if (version < PostgresVersion(9, 6, 0)) {
result = con.TryQuery("SELECT pg_is_in_recovery(), pg_export_snapshot()");
if (result) {
auto in_recovery = result->GetBool(0, 0);
if (!in_recovery) {
gstate.snapshot = result->GetString(0, 1);
}
}
return;
}

result =
con.TryQuery("SELECT pg_is_in_recovery(), pg_export_snapshot(), (select count(*) from pg_stat_wal_receiver)");
con.TryQuery("SELECT pg_export_snapshot()");
if (result) {
auto in_recovery = result->GetBool(0, 0) || result->GetInt64(0, 2) > 0;
gstate.snapshot = "";
if (!in_recovery) {
gstate.snapshot = result->GetString(0, 1);
}
return;
gstate.snapshot = result->GetString(0, 0);
}
}

Expand Down Expand Up @@ -324,7 +305,7 @@ static unique_ptr<GlobalTableFunctionState> PostgresInitGlobalState(ClientContex
result->collection->InitializeScan(result->scan_state);
} else {
// we create a transaction here, and get the snapshot id to enable transaction-safe parallelism
PostgresGetSnapshot(bind_data.version, bind_data, *result);
PostgresGetSnapshot(bind_data, *result);
}
return std::move(result);
}
Expand Down