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optimize memory allocation of changesets with many small strings #5614

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merged 2 commits into from
Jun 24, 2022
Merged

optimize memory allocation of changesets with many small strings #5614

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ade8cb4
optimize memory allocation of changesets with many small strings
ironage Jun 22, 2022
bfc9de9
let strings manage their own capacity past the first 1024
ironage Jun 23, 2022
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,7 @@
### Fixed
* <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)
* Fix a UBSan failure when mapping encrypted pages.
* Improved performance of sync clients during integration of changesets with many small strings (totalling > 1024 bytes per changeset) on iOS 14, and devices which have restrictive or fragmented memory. ([#5614](https://github.com/realm/realm-core/issues/5614))

### Breaking changes
* None.
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7 changes: 6 additions & 1 deletion src/realm/sync/changeset.hpp
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Expand Up @@ -539,7 +539,12 @@ inline StringData Changeset::string_data() const noexcept

inline StringBufferRange Changeset::append_string(StringData string)
{
m_string_buffer->reserve(1024); // we expect more strings
// We expect more strings. Only do this at the beginning because until C++20, reserve
// will shrink_to_fit if the request is less than the current capacity.
constexpr size_t small_string_buffer_size = 1024;
if (m_string_buffer->capacity() < small_string_buffer_size) {
m_string_buffer->reserve(small_string_buffer_size);
}
size_t offset = m_string_buffer->size();
m_string_buffer->append(string.data(), string.size());
return StringBufferRange{uint32_t(offset), uint32_t(string.size())};
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