feat: Mark truncated log lines with identifier #18262
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chaudum
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Jun 27, 2025
| @@ -3720,6 +3720,10 @@ The `limits_config` block configures global and per-tenant limits in Loki. The v | |||
| # CLI flag: -distributor.max-line-size-truncate | |||
| [max_line_size_truncate: <boolean> | default = false] | |||
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| # Identifier that is added at the end of a truncated log line. | |||
| # CLI flag: -distributor.max-line-size-truncate-identifier | |||
| [max_line_size_truncate_identifier: <string> | default = ""] | |||
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Alternative naming proposal:
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| [max_line_size_truncate_identifier: <string> | default = ""] | |
| [max_line_size_truncate_suffix: <string> | default = ""] |
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This PR adds the possibility to add an identifier as suffix for truncated log lines, such as `[...]` so that truncated log lines are easier to spot and identify when querying them. Signed-off-by: Christian Haudum <christian.haudum@gmail.com>
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| var truncatedSamples, truncatedBytes int | ||
| for i, e := range stream.Entries { | ||
| if maxSize := vContext.maxLineSize; maxSize != 0 && len(e.Line) > maxSize { | ||
| stream.Entries[i].Line = e.Line[:maxSize] | ||
| truncateTo := maxSize - len(suffix) |
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can we add a test? :)
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given this is hotpath, should we have the suffix logic in its own branch only when len(suffix) > 0?
| continue | ||
| } | ||
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| stream.Entries[i].Line = e.Line[:truncateTo] + suffix |
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i guess this also allocs new slice
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Yes, it creates a new string. There are benchmarks in the original truncation PR, which show that there is very little overhead, though.
Signed-off-by: Christian Haudum <christian.haudum@gmail.com>
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Jun 30, 2025
While truncated JSON log lines are usually easy to identify (because the JSON becomes invalid), it is not always the case with other plain text log lines. This PR adds the possibility to add an identifier as suffix for truncated log lines, such as `[...]` so that truncated log lines are easier to spot and identify when querying them. Signed-off-by: Christian Haudum <christian.haudum@gmail.com> (cherry picked from commit 0ee8e76)
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What this PR does / why we need it:
While truncated JSON log lines are usually easy to identify (because the JSON becomes invalid), it is not always the case with other plain text log lines.
This PR adds the possibility to add an identifier as suffix for truncated log lines, such as
[...]so that truncated log lines are easier to spot and identify when querying them.A truncation identifier has almost been implemented with the initial truncation PR (#4051). This implementation is essentially the same.