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a89d270cd3
The gotextdiff/myers library uses the naive Myers algorithm variant that stores the full edit trace, resulting in O((M+N)^2) space complexity. For machine configs with large inline K8s manifests (thousands of lines), this causes massive memory spikes — e.g., 80K lines allocates ~98 GB and gets OOM-killed. Replace it with neticdk/go-stdlib/diff/myers which implements the linear-space Myers variant (divide-and-conquer). Memory usage drops from ~25 GB to ~8 MB for 40K-line inputs. The diff output format is unchanged (unified diff with @@ hunks). Co-authored-by: Artem Chernyshev <artem.chernyshev@talos-systems.com> Co-authored-by: Oguz Kilcan <oguz.kilcan@siderolabs.com> Signed-off-by: Utku Ozdemir <utku.ozdemir@siderolabs.com>
59 lines
2.0 KiB
Go
59 lines
2.0 KiB
Go
// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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// file, You can obtain one at http://mozilla.org/MPL/2.0/.
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// Package diff provides a memory-safe unified diff computation.
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package diff
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import (
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"bytes"
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"fmt"
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"strings"
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"github.com/neticdk/go-stdlib/diff/myers"
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)
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// MaxLines is the maximum total number of lines (old + new) for which a full
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// structural diff is computed. Beyond this the diff is summarized because no
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// human can meaningfully review it and the algorithmic cost becomes prohibitive.
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const MaxLines = 75_000
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// Compute returns a unified diff (without the --- / +++ header) between two
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// byte slices. For inputs whose combined line count exceeds MaxLines it returns
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// a short summary instead.
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func Compute(previousData, newData []byte) (string, error) {
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if bytes.Equal(previousData, newData) {
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return "", nil
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}
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prevLines := bytes.Count(previousData, []byte("\n"))
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newLines := bytes.Count(newData, []byte("\n"))
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if prevLines+newLines > MaxLines {
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return fmt.Sprintf("@@ -%d,%d +%d,%d @@ diff too large to display\n", 1, prevLines, 1, newLines), nil
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}
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result, err := myers.Diff(string(previousData), string(newData),
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myers.WithUnifiedFormatter(),
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myers.WithLinearSpace(true),
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// Disable the library's standard-Myers and LCS fallback paths:
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// - Standard Myers (< smallInputThreshold) is O((N+M)²) when inputs are asymmetric.
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// - LCS (> largeInputThreshold) is O(N*M) for the DP table.
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// By setting these to 0 and MaxLines respectively, only Hirschberg's
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// O(N+M) linear-space algorithm runs. Our MaxLines guard above ensures
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// inputs never exceed largeInputThreshold.
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myers.WithSmallInputThreshold(0),
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myers.WithLargeInputThreshold(MaxLines),
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)
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if err != nil {
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return "", err
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}
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// Strip the "--- a\n+++ b\n" header that the library always prepends.
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if after, ok := strings.CutPrefix(result, "--- a\n+++ b\n"); ok {
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result = after
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}
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return result, nil
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}
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