Miller Files

The headline for this release is across-the-board runtime improvements.

For details, please see https://miller.readthedocs.io/en/latest/performance/#allocationgc-optimizations-june-2026.

Performance

• Lazy per-record hashing: ~15-30% faster on common workloads by @johnkerl in https://github.com/johnkerl/miller/pull/2081
• Batch-arena field allocation for line-based readers by @johnkerl in https://github.com/johnkerl/miller/pull/2082
• Batch-allocate per-record objects; reuse CSV-writer field buffer by @johnkerl in https://github.com/johnkerl/miller/pull/2083
• Pool DSL stack frames across records (~8-9% perf on mlr put) by @johnkerl in https://github.com/johnkerl/miller/pull/2086
• Pool DSL stack-frame sets across UDF/subroutine calls (~31% perf on function-heavy mlr put) by @johnkerl in https://github.com/johnkerl/miller/pull/2088
• Drop redundant deep-copy of UDF return values (~3-16% perf on UDFs in mlr put) by @johnkerl in https://github.com/johnkerl/miller/pull/2089
• Bind scalar locals/params by reference, not by copy (~4-9% on DSL) by @johnkerl in https://github.com/johnkerl/miller/pull/2090
• docs: add "Allocation/GC optimizations: June 2026" performance section by @johnkerl in https://github.com/johnkerl/miller/pull/2091

Features

• Add --omd-aligned flag for column-padded markdown output by @johnkerl in https://github.com/johnkerl/miller/pull/2057
• Default to "cat" verb when none is supplied by @johnkerl in https://github.com/johnkerl/miller/pull/2060

Bug fixes

• Fix mlr -s shebang doc and reject arrays/maps in contains/index by @johnkerl in https://github.com/johnkerl/miller/pull/2058
• Fix data dropped from ragged implicit-header TSV/CSV-lite input by @johnkerl in https://github.com/johnkerl/miller/pull/2059
• Fix column alignment for wide and combining Unicode chars (#1520, [#379]) by @johnkerl in https://github.com/johnkerl/miller/pull/2061
• Apply join prefixes/rename to unpaired records (#1821) by @johnkerl in https://github.com/johnkerl/miller/pull/2062
• Fix PPRINT alignment with multi-character OFS (#1819) by @johnkerl in https://github.com/johnkerl/miller/pull/2063
• Allow empty-string keys in JSON and YAML input by @johnkerl in https://github.com/johnkerl/miller/pull/2068
• Update ubuntu/python versions in .readthedocs.yaml by @johnkerl in https://github.com/johnkerl/miller/pull/2092
• Fix exponential memory use when chaining seqgen (#2072) by @johnkerl in https://github.com/johnkerl/miller/pull/2094

Dependency updates

• Bump goreleaser/goreleaser-action from 7.0.0 to 7.1.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2045
• Bump goreleaser/goreleaser-action from 7.1.0 to 7.2.1 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2047
• Bump github.com/mattn/go-isatty from 0.0.21 to 0.0.22 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2048
• Bump github.com/klauspost/compress from 1.18.5 to 1.18.6 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2050
• Bump github/codeql-action from 4.35.2 to 4.35.3 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2051
• Bump github/codeql-action from 4.35.3 to 4.35.4 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2052
• Bump golang.org/x/term from 0.42.0 to 0.43.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2055
• Bump golang.org/x/text from 0.36.0 to 0.37.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2054
• Bump github/codeql-action from 4.35.4 to 4.35.5 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2056
• Bump goreleaser/goreleaser-action from 7.2.1 to 7.2.2 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2064
• Bump github.com/lestrrat-go/strftime from 1.1.1 to 1.2.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2065
• Bump github/codeql-action from 4.35.5 to 4.36.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2066
• Bump golang.org/x/sys from 0.44.0 to 0.45.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2067
• Bump github/codeql-action from 4.36.0 to 4.36.1 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2069
• Bump github/codeql-action from 4.36.1 to 4.36.2 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2070
• Bump golang.org/x/text from 0.37.0 to 0.38.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2073
• Bump golang.org/x/term from 0.43.0 to 0.44.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2074
• Bump golang.org/x/sys from 0.45.0 to 0.46.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2075
• Bump pault.ag/go/debian from 0.19.0 to 0.20.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2077
• Bump pault.ag/go/debian from 0.20.0 to 0.21.0 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2078
• Bump github.com/cloudflare/circl from 1.6.2 to 1.6.3 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2079
• Bump actions/checkout from 6 to 7 by @dependabot[bot] in https://github.com/johnkerl/miller/pull/2080

Full Changelog: https://github.com/johnkerl/miller/compare/v6.18.1...v6.19.0