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Clarify documentation of RIStorageServer.slot_testv_and_readv_and_writev. fixes #1744

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david-sarah 2012-06-13 16:51:35 +00:00
parent ef2db56104
commit daa24bce8b
1 changed files with 23 additions and 12 deletions
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35
src/allmydata/interfaces.py
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@ -159,10 +159,18 @@ class RIStorageServer(RemoteInterface):
tw_vectors=TestAndWriteVectorsForShares,
r_vector=ReadVector,
):
"""General-purpose test-and-set operation for mutable slots. Perform
a bunch of comparisons against the existing shares. If they all pass,
then apply a bunch of write vectors to those shares. Then use the
read vectors to extract data from all the shares and return the data.
"""
General-purpose test-read-and-set operation for mutable slots:
(1) For submitted shnums, compare the test vectors against extant
shares, or against an empty share for shnums that do not exist.
(2) Use the read vectors to extract "old data" from extant shares.
(3) If all tests in (1) passed, then apply the write vectors
(possibly creating new shares).
(4) Return whether the tests passed, and the "old data", which does
not include any modifications made by the writes.
The operation does not interleave with other operations on the same
shareset.
This method is, um, large. The goal is to allow clients to update all
the shares associated with a mutable file in a single round trip.
@ -187,9 +195,9 @@ class RIStorageServer(RemoteInterface):
Each share can have a separate test vector (i.e. a list of
comparisons to perform). If all vectors for all shares pass, then all
writes for all shares are recorded. Each comparison is a 4-tuple of
(offset, length, operator, specimen), which effectively does a bool(
(read(offset, length)) OPERATOR specimen ) and only performs the
write if all these evaluate to True. Basic test-and-set uses 'eq'.
(offset, length, operator, specimen), which effectively does a
bool( (read(offset, length)) OPERATOR specimen ) and only performs
the write if all these evaluate to True. Basic test-and-set uses 'eq'.
Write-if-newer uses a seqnum and (offset, length, 'lt', specimen).
Write-if-same-or-newer uses 'le'.
@ -199,7 +207,11 @@ class RIStorageServer(RemoteInterface):
The write vector will be applied to the given share, expanding it if
necessary. A write vector applied to a share number that did not
exist previously will cause that share to be created.
exist previously will cause that share to be created. Write vectors
must not overlap (if they do, this will either cause an error or
apply them in an unspecified order). Duplicate write vectors, with
the same offset and data, are currently tolerated but are not
desirable.
In Tahoe-LAFS v1.8.3 or later (except 1.9.0a1), if you send a write
vector whose offset is beyond the end of the current data, the space
@ -232,9 +244,9 @@ class RIStorageServer(RemoteInterface):
than the size of the data after applying all write vectors.
The read vector is used to extract data from all known shares,
*before* any writes have been applied. The same vector is used for
all shares. This captures the state that was tested by the test
vector.
*before* any writes have been applied. The same read vector is used
for all shares. This captures the state that was tested by the test
vector, for extant shares.
This method returns two values: a boolean and a dict. The boolean is
True if the write vectors were applied, False if not. The dict is
@ -250,7 +262,6 @@ class RIStorageServer(RemoteInterface):
Note that the nodeid here is encoded using the same base32 encoding
used by Foolscap and allmydata.util.idlib.nodeid_b2a().
"""
return TupleOf(bool, DictOf(int, ReadData))