investigate buffering data before gzipping

Some high cpu usage was observed in the docappender when writing to the gzip writer.

Investigate if we need to buffer data before writing

Start by locating the docappender path that writes to the gzip writer and reproduce or profile the high CPU usage described in the issue. Done means determining whether buffering is needed before gzip writes and documenting or implementing the chosen change with evidence that CPU usage is addressed.

Written by the indexing model from the issue text.