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doc(state): explain how Zebra stays below Windows open file limits (#3590)

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teor 2022-02-24 16:23:21 +10:00 committed by GitHub
parent 957a150254
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1 changed files with 27 additions and 14 deletions
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41
zebra-state/src/service/finalized_state/disk_db.rs
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@ -273,30 +273,43 @@ impl DiskDb {
///
/// If the open file limit can not be increased to `MIN_OPEN_FILE_LIMIT`.
fn increase_open_file_limit() -> u64 {
// `increase_nofile_limit` doesn't do anything on Windows in rlimit 0.7.0.
// Zebra mainly uses TCP sockets (`zebra-network`) and low-level files
// (`zebra-state` database).
//
// On Unix-based platforms, `increase_nofile_limit` changes the limit for
// both database files and TCP connections.
//
// But it doesn't do anything on Windows in rlimit 0.7.0.
//
// On Windows, the default limits are:
// - 512 high-level stream I/O files (via the C standard functions),
// - 8192 low-level I/O files (via the Unix C functions), and
// - 1000 TCP Control Block entries (network connections).
//
// On Windows, the default limit is:
// - 512 high-level stream I/O files (via the C standard functions), and
// - 8192 low-level I/O files (via the Unix C functions).
// https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/setmaxstdio?view=msvc-160#remarks
// http://smallvoid.com/article/winnt-tcpip-max-limit.html
//
// If we need more high-level I/O files on Windows,
// use `setmaxstdio` and `getmaxstdio` from the `rlimit` crate:
// https://docs.rs/rlimit/latest/rlimit/#windows
// `zebra-state`'s `IDEAL_OPEN_FILE_LIMIT` is much less than
// the Windows low-level I/O file limit.
//
// Then panic if `setmaxstdio` fails to set the minimum value,
// and `getmaxstdio` is below the minimum value.
// The [`setmaxstdio` and `getmaxstdio`](https://docs.rs/rlimit/latest/rlimit/#windows)
// functions from the `rlimit` crate only change the high-level I/O file limit.
//
// `zebra-network`'s default connection limit is much less than
// the TCP Control Block limit on Windows.
// We try setting the ideal limit, then the minimum limit.
let current_limit = match increase_nofile_limit(DiskDb::IDEAL_OPEN_FILE_LIMIT) {
Ok(current_limit) => current_limit,
Err(limit_error) => {
// These errors can happen due to sandboxing or unsupported system calls,
// even if the file limit is high enough.
info!(
?limit_error,
min_limit = ?DiskDb::MIN_OPEN_FILE_LIMIT,
ideal_limit = ?DiskDb::IDEAL_OPEN_FILE_LIMIT,
"unable to increase the open file limit, \
assuming Zebra can open a minimum number of files"
?limit_error,
min_limit = ?DiskDb::MIN_OPEN_FILE_LIMIT,
ideal_limit = ?DiskDb::IDEAL_OPEN_FILE_LIMIT,
"unable to increase the open file limit, \
assuming Zebra can open a minimum number of files"
);
return DiskDb::MIN_OPEN_FILE_LIMIT;