Add flush_every_n_blocks config option to BufWriter generators #1683
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What does this PR do?
Adds flush_every_n_blocks to traditional and logrotate generators. This is designed to be used in conjunction with block-based throttling to ensure that blocks are still flushed regularly.
Motivation
BufWriter generally only writes out to disk once its capacity is full (or on log rotate). For standard usage of lading, this works fine since the capacity is set at the maximum throttler capacity (in bytes), which lading trires its best to run at, so it flushes ~every second. However, for block-based throttling (and varying block sizes) it's less likely that 1 second of blocks fills the maximum possible bytes capacity for those blocks (blocks per second times max block size), so having a config option to manually flush every few blocks ensures regular flush intervals.
Related issues
Follow up of #1675