To pause/resume the backup workers, the fdbbackup command will write to the
backupPausedKey. Then backup workers noticed the value of the key has been
changed and stops/resumes pulling from TLog.
A mutation log's version batch data can be split into multiple blocks, and some
of the blocks can be spread across two mutation logs. Thus, the decoder needs
copy unfinished version batch data from previous file progress to the next one.
After reading a new block, all mutations are sorted by version again, which
can invalidate previously tuple. As a result, the decoded file will miss some
of the mutations.
In the old mutation logs, a version's mutations are serialized as a buffer.
Then the buffer is split into smaller chunks, e.g., 10000 bytes each. When
writting chunks to the final mutation log file, these chunks can be flushed
out of order. For instance, the (version, chunck_part) can be in the order of
(3, 0), (4, 0), (3, 1). As a result, the decoder must read forward to find all
chunks of data for a version.
Another complication is that the files are organized into blocks, where (3, 1)
can be in a subsequent block. This change checks the value size for each
version, if the size is smaller than the right size, the decoder will look
for the missing chucks in the next block.
If a log file's progress is not saved, a new log file will be generated
with the same begin version. Then we can have a file that contains a subset
of contents in another log file. During restore, we should filter out files
that their contents are subset of other files.
The idea being that we keep around a TLSConfig that the configuration
that the user has provided, and then when we want to intialize an SSL
context, we ask the TLSConfig to load all certificates and return us a
LoadedTLSConfig that is a concrete set of certificate bytes in memory.
initTLS now just takes the in-memory bytes and applies them to the ssl
context.
This is a large refactor to lead up into certificate refeshing, where we
will periodically check for changes to the certificates, and then
re-load them and apply them to a new SSL context.
When a value (i.e., mutations for a version) is large, it will be split into
multiple key value pairs. This is not handled previously and fixing it also
consolidate the interface of DecodeProgress.
For each mutation, its version, sub-version, and size are prefixed with big
endian representation. This is required, especially for the first version
variable, because we use 0xFF for padding purpose. A little endian version
number can easily collide with 0xFF, while big endian is guaranteed to have
0x00 as the first byte.
Meng Xu