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subscriber: don't use SmallVecs for filter fields #1568

Merged
merged 2 commits into from
Sep 15, 2021
Merged

subscriber: don't use SmallVecs for filter fields #1568

merged 2 commits into from
Sep 15, 2021

Commits on Sep 15, 2021

  1. add tests for printing the size of filters 

    Signed-off-by: Eliza Weisman <eliza@buoyant.io>
    @hawkw
    hawkw committed Sep 15, 2021
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  2. subscriber: don't use SmallVecs for filter fields 

    The `DirectiveSet` type used in `EnvFilter` and `Targets` uses
`SmallVec` to store the filtering directives when the `SmallVec` feature
is enabled. This is intended to improve the performance of iterating
over small sets of directives, by avoiding a heap pointer dereference.

PR #1550 changed the directives themselves to also use `SmallVec` for
storing _field_ filters. This was intended to make the same optimization
for field filters. However, it had unintended consequences: an empty
`SmallVec` is an array of `T` items (plus metadata), while an empty
`Vec` is just a couple of words. Since _most_ filters don't have field
filters, this meant that we were suddenly using a lot more space to
store...nothing. This made `EnvFilter`s _much_ larger, causing problems
for some users (see #1567).

This branch undoes the change to `SmallVec` for field name/value
filters. This takes the size of an `EnvFilter` from 5420 bytes back down
to 1272 bytes.

Fixes #1567
    @hawkw
    hawkw committed Sep 15, 2021
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