[Bug 199584] Handbook, hast.conf manpage, and wiki inconsistency on default replication method
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bugzilla-noreply at freebsd.org
Tue Apr 21 16:37:13 UTC 2015
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199584
Bug ID: 199584
Summary: Handbook, hast.conf manpage, and wiki inconsistency on
default replication method
Product: Documentation
Version: Latest
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: Documentation
Assignee: freebsd-doc at FreeBSD.org
Reporter: me at waltonhoops.com
The Handbook for HAST indicates that if no replication method is specified,
fullsync is used. The man page for hast.conf specifies memsync as the default.
Most confusing, the wiki states that only memsync is implemented, but fullsync
is the default.
Relevant excerpts:
Handbook:
fullsync: This mode reports a write operation as completed when both the local
write and the remote write complete. This is the safest and the slowest
replication mode. This mode is the default.
hast.conf(5):
(final line under the memsync replication mode)
The memsync replication mode is the default.
Wiki:
Currently only the first replication mode described below is supported, but
other replication modes are described as well to show the difference and to
note desire for implementing them.
memsync - Report write operation as completed when local write completes
and when remote node acknowledges data arrival, but before actually storing the
data. The data on remote node will be stored directly after sending answer.
This mode is intended to reduce latency, but still provide very good
reliability. The only situation where some small amount of data could be lost
is when data is stored on primary and sent to secondary. Secondary then
acknowledges data and primary reports success to an application. Before data is
really stored on secondary node, it goes down for some period of time. Before
secondary returns, primary node dies entirely. Secondary node comes back to
life and becomes new primary. Unfortunately some small amount of data that was
confirmed to be safe to the application was lost. The risk of such situation is
very low. The memsync replication mode is currently not implemented.
fullsync - Report write operation as completed when local write completes
and when remote write completes. This is the safest and the slowest replication
mode. The fullsync replication mode is the default.
async - Report write operation as completed when local write completes.
This is the fastest and the most dangerous replica- tion mode. This mode should
be used when replicating to a distant node where latency is too high for other
modes. The async replication mode is currently not implemented.
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