![[wl_io_twophasefilewrite.png|256]] - **Description**: Waiting for an OS `write()` of a two-phase state file (stored in the `pg_twophase/` directory). This is a critical disk I/O path because handling a distributed `PREPARE TRANSACTION` requires strict durability, mandating an immediate `fsync()` after the write. - **Resources**: [[Disk IO]], [[CPU]]