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GC-related optimizations #2

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@casept casept commented May 7, 2024

  • Remove manual GC calls, these shouldn't be needed anymore as the Go runtime now manages low-memory situations better
  • Significantly reduce the amount of garbage generated in hot functions, leading to speedups of about 25%

casept added 5 commits May 7, 2024 04:11
@casept
Remove needless runtime.GC() calls
9e8c265
@casept
Speed up parsing significantly
d7666d5 
Passing the Fields interface into the readX functions results
in the passed-in struct being copied, creating an object that
needs to be cleaned up by GC later.

This results in a large part of program runtime being spent on
GC, as this function is used in many hot functions, such as
createStopTime().

According to pprof, removing these copies speeds up the entire
program by about 14%, and reduces the amount of garbage objects generated
by over 25%.
@casept
Reduce garbage created by getTime
7595a2c 
This function is on a hot path and previosuly used
string.Split, which allocates a string slice and therefore
produces a lot of garbage.

Replace with strings.Cut, which doesn't allocate.
@casept
Don't return entire StopTime object from createStopTime
d961f6e 
The sole caller only uses one field, and by returning this field
directly we allow Go's escape analysis to do it's thing and avoid
a costly heap allocation. According to pprof, this cuts out
several million allocations when parsing the German GTFS dataset.

This function is not exported, therefore this change does not alter the public API.
@casept
Optimize away headsign allocation in parseStopTimes
6889255 
The logic to apply custom headsigns seems broken anyways,
as the ID is negative and the field is not marked required,
leading to getString() always returning the empty string.

According to pprof, this reduces GC usage by 25%
and speeds up gtfstidy by 6%.
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