Save Memory on Large Repository Metadata Blob Writes #74693
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Extracted the chunked output stream logic from elastic#74313 and added tests for it to make it easier to review.
This PR adds a new API for doing streaming serialization writes to a repository to enable repository metadata of arbitrary size and at bounded memory during writing. The existing write-APIs require knowledge of the eventual blob size beforehand. This forced us to materialize the serialized blob in memory before writing, costing a lot of memory in case of e.g. very large `RepositoryData` (and limiting us to `2G` max blob size). With this PR the requirement to fully materialize the serialized metadata goes away and the memory overhead becomes completely bounded by the outbound buffer size of the repository implementation. As we move to larger repositories this makes master node stability a lot more predictable since writing out `RepositoryData` does not take as much memory any longer (same applies to shard level metadata), enables aggregating multiple metadata blobs into a single larger blobs without massive overhead and removes the 2G size limit on `RepositoryData`.
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This PR adds a new API for doing streaming serialization writes to a repository to enable repository metadata of arbitrary size and at bounded memory during writing.
The existing write-APIs require knowledge of the eventual blob size beforehand. This forced us to materialize the serialized blob in memory before writing, costing a lot of memory in case of e.g. very large
RepositoryData(and limiting us to2Gmax blob size).With this PR the requirement to fully materialize the serialized metadata goes away and the memory overhead becomes completely bounded by the outbound buffer size of the repository implementation.
As we move to larger repositories this makes master node stability a lot more predictable since writing out
RepositoryDatadoes not take as much memory any longer (same applies to shard level metadata), enables aggregating multiple metadata blobs into a single larger blobs without massive overhead and removes the 2G size limit onRepositoryData.backport of #74313 and #74620