fix(backtest): bound every log tail to the final 256 KB - #19
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The live /tail endpoint read entire log files into memory on every poll:
_tail_dir_log and get_tail's run.log block called a whole-file reader,
then decoded and split the result. A Strategy Tester log grows to
gigabytes WHILE the run that is being polled writes it, so each poll
allocated the file plus a decoded copy plus a line list — 45-65 s per
call measured against a 1.9 GB log, with the GIL held through the decode.
Every thread in the process stalled behind it: /ping took 25-50 s, the
container healthcheck flapped, clients timed out, and a healthy terminal
was indistinguishable from a wedged one. (_tail_terminal_log, the
failure-path tail, had the same unbounded read.)
_read_tail_text seeks to the final 256 KB, aligned to a 2-byte boundary
so UTF-16 code units stay intact, sniffs UTF-16 from a BOM or a NUL
second byte, and drops the truncated first line of a mid-file window.
Both tail helpers and the run.log block now use it; whole-file reads
remain only where the whole file is genuinely needed (INI parse, report
parse).
_tail_dir_log also inherits the two picker rules _tail_terminal_log
already had and it predated: newest by mtime, never metaeditor.log —
the alphabetical pick returned a stale compile log ('m' > '2') instead
of the run being polled.
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What
The live
/tailendpoint read entire log files into memory on every poll:_tail_dir_logandget_tail's run.log block called a whole-file reader, then decoded and split the result.A Strategy Tester log grows to gigabytes while the run being polled writes it, so each poll allocated the file + a decoded copy + a line list — measured 45–65 s per call against a 1.9 GB log, with the GIL held through the decode. Every thread in the process stalled behind it:
/pingtook 25–50 s, the container healthcheck flapped, clients timed out, and a healthy terminal was indistinguishable from a wedged one._tail_terminal_log(the failure-path tail) had the same unbounded read.Fix
_read_tail_text: seek to the final 256 KB, 2-byte aligned so UTF-16 code units stay intact; sniff UTF-16 from a BOM or NUL second byte; drop the truncated first line of a mid-file window. Used by both tail helpers and the run.log block._tail_dir_loginherits the two picker rules_tail_terminal_logalready had and it predated: newest by mtime, nevermetaeditor.log(the alphabetical pick returned a stale compile log — 'm' > '2' — instead of the run being polled).Tests
12 new tests: bounded-window correctness (truncated first line dropped, UTF-16 alignment via a non-ASCII log, small-file passthrough, missing file), bounded
_tail_terminal_log, and_tail_dir_log's mtime pick / metaeditor exclusion / bounded read / empty dir. Full suite: 432 passed.