Optimize parse_relfilename() function.

Compiling a Regex is very expensive, so let's not do it on every
invocation. This was consuming a big fraction of the time in creating
a new base backup at "zenith pg create". This commits brings down the
time to run "zenith pg create" on a freshly created repository from
about 2 seconds to 1 second.

It's not worth spending much effort on optimizing things at this stage
in general, but might as well pick low-hanging fruit like this.

Cargo.lock

@@ -1359,6 +1359,7 @@ dependencies = [
  "chrono",
  "crc32c",
  "hex",
+ "lazy_static",
  "log",
  "rand",
  "regex",

postgres_ffi/Cargo.toml

@@ -15,6 +15,7 @@ byteorder = "1.4.3"
 anyhow = "1.0"
 crc32c = "0.6.0"
 hex = "0.4.3"
+lazy_static = "1.4"
 log = "0.4.14"
 thiserror = "1.0"
 workspace_hack = { path = "../workspace_hack" }

postgres_ffi/src/relfile_utils.rs

@@ -2,6 +2,7 @@
 //! Common utilities for dealing with PostgreSQL relation files.
 //!
 use crate::pg_constants;
+use lazy_static::lazy_static;
 use regex::Regex;
 
 #[derive(Debug, Clone, thiserror::Error, PartialEq)]
@@ -63,9 +64,11 @@ pub fn forknumber_to_name(forknum: u8) -> Option<&'static str> {
 /// See functions relpath() and _mdfd_segpath() in PostgreSQL sources.
 ///
 pub fn parse_relfilename(fname: &str) -> Result<(u32, u8, u32), FilePathError> {
-    let re = Regex::new(r"^(?P<relnode>\d+)(_(?P<forkname>[a-z]+))?(\.(?P<segno>\d+))?$").unwrap();
-
-    let caps = re.captures(fname).ok_or(FilePathError::InvalidFileName)?;
+    lazy_static! {
+        static ref RELFILE_RE: Regex =
+            Regex::new(r"^(?P<relnode>\d+)(_(?P<forkname>[a-z]+))?(\.(?P<segno>\d+))?$").unwrap();
+    }
+    let caps = RELFILE_RE.captures(fname).ok_or(FilePathError::InvalidFileName)?;
 
     let relnode_str = caps.name("relnode").unwrap().as_str();
     let relnode = relnode_str.parse::<u32>()?;