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constants: reorder stuff, add comments

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This commit is contained in:
Thomas Waldmann 2022-08-11 17:36:57 +02:00
parent a18a9df364
commit a7bc1f88c1
1 changed files with 20 additions and 18 deletions
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38
src/borg/constants.py
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@ -30,15 +30,6 @@
# forcing to 0o100XXX later
STDIN_MODE_DEFAULT = 0o660
CACHE_TAG_NAME = "CACHEDIR.TAG"
CACHE_TAG_CONTENTS = b"Signature: 8a477f597d28d172789f06886806bc55"
# A large, but not unreasonably large segment size. Always less than 2 GiB (for legacy file systems). We choose
# 500 MiB which means that no indirection from the inode is needed for typical Linux file systems.
# Note that this is a soft-limit and can be exceeded (worst case) by a full maximum chunk size and some metadata
# bytes. That's why it's 500 MiB instead of 512 MiB.
DEFAULT_MAX_SEGMENT_SIZE = 500 * 1024 * 1024
# in borg < 1.3, this has been defined like this:
# 20 MiB minus 41 bytes for a PUT header (because the "size" field in the Repository includes
# the header, and the total size was set to precisely 20 MiB for borg < 1.3).
@ -49,12 +40,21 @@
# borg < 1.3, but this is not expected to cause any issues.
MAX_OBJECT_SIZE = MAX_DATA_SIZE + 41 + 8 # see assertion at end of repository module
# how many metadata stream chunk ids do we store into a "pointer chunk" of the ArchiveItem.item_ptrs list?
IDS_PER_CHUNK = 3 # MAX_DATA_SIZE // 40
# How many segment files borg puts into a single directory by default.
DEFAULT_SEGMENTS_PER_DIR = 1000
# A large, but not unreasonably large segment size. Always less than 2 GiB (for legacy file systems). We choose
# 500 MiB which means that no indirection from the inode is needed for typical Linux file systems.
# Note that this is a soft-limit and can be exceeded (worst case) by a full maximum chunk size and some metadata
# bytes. That's why it's 500 MiB instead of 512 MiB.
DEFAULT_MAX_SEGMENT_SIZE = 500 * 1024 * 1024
# repo config max_segment_size value must be below this limit to stay within uint32 offsets:
MAX_SEGMENT_SIZE_LIMIT = 2**32 - MAX_OBJECT_SIZE
# how many metadata stream chunk ids do we store into a "pointer chunk" of the ArchiveItem.item_ptrs list?
IDS_PER_CHUNK = 3 # MAX_DATA_SIZE // 40
# have one all-zero bytes object
# we use it at all places where we need to detect or create all-zero buffers
zeros = bytes(MAX_DATA_SIZE)
@ -70,19 +70,18 @@
# repo.list() / .scan() result count limit the borg client uses
LIST_SCAN_LIMIT = 100000
DEFAULT_SEGMENTS_PER_DIR = 1000
FD_MAX_AGE = 4 * 60 # 4 minutes
CHUNK_MIN_EXP = 19 # 2**19 == 512kiB
CHUNK_MAX_EXP = 23 # 2**23 == 8MiB
HASH_WINDOW_SIZE = 0xFFF # 4095B
HASH_MASK_BITS = 21 # results in ~2MiB chunks statistically
# chunker algorithms
CH_BUZHASH = "buzhash"
CH_FIXED = "fixed"
# buzhash chunker params
CHUNK_MIN_EXP = 19 # 2**19 == 512kiB
CHUNK_MAX_EXP = 23 # 2**23 == 8MiB
HASH_WINDOW_SIZE = 0xFFF # 4095B
HASH_MASK_BITS = 21 # results in ~2MiB chunks statistically
# defaults, use --chunker-params to override
CHUNKER_PARAMS = (CH_BUZHASH, CHUNK_MIN_EXP, CHUNK_MAX_EXP, HASH_MASK_BITS, HASH_WINDOW_SIZE)
@ -159,6 +158,9 @@ class KeyType:
BLAKE2CHPOREPO = 0x41
CACHE_TAG_NAME = "CACHEDIR.TAG"
CACHE_TAG_CONTENTS = b"Signature: 8a477f597d28d172789f06886806bc55"
REPOSITORY_README = """This is a Borg Backup repository.
See https://borgbackup.readthedocs.io/
"""