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feat: append mlog in fixed-size blocks using log_appender #418
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acelyc111
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src/dist/replication/lib/duplication/test/load_from_private_log_test.cpp
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feat: append mlog in fixed-size blocks using log_appender
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The current
mutation_logimplementation is unfriendly with such case:There're some writes being flushed into the disk, in the meantime, new incoming writes are pending in the
log_blockwaiting to be flushed.As the pending
log_blockgrows, it could be considerably large (like tens of MB) which is unfriendly for both replica recovery and duplication. I've met a bug while testing duplication that reading a large log block may cause tcmalloc to allocate an inaccessible memory.This PR limits the log block to 1MB using
log_appender, reduces the possibility of large block related bug.log_appenderis a buffer for multiple log blocks. This PR doesn't change the behavior that all the pending writes will be flushed to disk (mutation_log::commit_pending_mutations), no matter how large the size is. What changed is only the size of the log-block, so that reading the log block can be more smooth, without allocating large memory buffer.While the buffered writes went flushed (which blocks another flush), the incoming writes will be buffered in a new
log_appender. The oldlog_appenderwill be removed.