Initial tests run comparing throughput when first populating and then
loading data into levelled and eleveledb.
The tests were run in series, populating first and then loading. The
population tests were run again in-between to try and add a roughly
even underlying volume into the stores.
The initial tests were run on on a quad core iMac with 8GB of RAM and a
fusion drive. Due to the limited footprint of the hardware, the number
of concurrent database instances was reduced to 12, rather than the 32
in the off0the-shelf leveldb test.
This allows for deleted journals to be retained for a period (the
waste_retnetion_period). The idea being that a backup strategy can
ensure that all journals are backed up, even ones created and removed
from within a backup period - so that any restore pont is possible.
This is also a pre-cursor to removing some of the PromptDelete
complexity from the Inker Clerk - all compactions can prompt deletion as
deletion is now deferred.
Leveled will now signal the need for a pause due to back-pressure, but
not actually pause itself. The hope is that in a riak implementation
this pause can be managed by the put_fsm, and so not lock the store.
Clena the API of Riak specific methods, and also resolve timing issue in
simple_server unit test. Previously this would end up with missing data
(and a lower sequence number after start) because of the penciller_clerk
timeout being relatively large in the context of this test. Now the
timeout has bene reduced the L0 slot is cleared by the time of the
close. To make sure an extra sleep has been added as a precaution to
avoid any intermittent issues.
Added a test of journal compaction with a registered snapshot and it
showed that the deleting of files did not correctly check the list of
registerd snapshots. Corrected.
Busted the hashtable in a Journal file, and demonstrated it can be fixed
by changing the extension name (no need to recover from backup if only
the hashtable is bust)
Changes the stratup otpions to a prolist to make it easier to get
environment variables as default.
Tried application:start - and completely baffled as to how to get this
to work.
There was some unpredictable performance in tests, that was related to
the amount of time it took the sft gen_server to accept a cast whihc
passed the levelzero_cache.
The response time looked to be broadly proportional to the size of the
cache - so it appeared to be an issue with passing the large object to
the process queue.
To avoid this, the penciller now instructs the SFT gen_server to
callback to the server for each tree in the cache in turn as it is
building the list from the cache. Each of these requests should be
reltaively short, and the processing in-between should space out the
requests so the Pencille ris not blocked from answering queries when
pompting a L0 write.
Stop the penciller from writing an empty file, when shutting down and
the L0 Cache is empty.
Also parameter fiddle to see impact of the Penciller changes.
Test added for the "retain" recovery strategy. This strategy makes sure
a full history of index changes is made so that if the Ledger is wiped
out, the Ledger cna be fully rebuilt from the Journal.
This exposed two journal compaction problems
- The BestRun selected did not have the source files correctly sorted in
order before compaction
- The compaction process incorrectly dealt with the KeyDelta object
left after a compaction - i.e. compacting twice the same key caused that
key history to be lost.
These issues have now been corrected.
The unit tests for the Penciller couldn't cope with the returned status
- and so would intermittently fail (after tightening the timeout on sft
check_ready.
The CDB file management server has distinct states, and was growing case
logic to prevent certain messages from being handled in ceratin states,
and to handle different messages differently. So this has now been
converted to a gen_fsm.
As part of resolving this, the space_clear_ondelete test has been
completed, and completing this revealed that the Penciller could not
cope with a change which emptied the ledger. So a series of changes has
been handled to allow it to smoothly progress to an empty manifest.
The no_hash option in CDB files became too hard to manage, in particular
the need to scan the whole file to find the last_key rather than cheat
and use the index. It has been removed for now.
The writing to the journal during journal compaction has now been
enhanced by a mput option on the CDB file write - so it can write each
batch as one pwrite operation.
Further progress towards the tidying up of basement tombstones in the
Ledger, with support added for key-listing to help with testing (and as
a potentially required feature).
The test is incomplete, but committing at this stage as the last commit
broke some tests (within the test code).
There are some outstanding questions about the handling of tombstones in
the Journal during compaction. There exists a condition whereby values
could return if a recent journal is compacted and tombstones are removed
(as they are no longer present), but older journals have not been
compacted. Now on stop/start - if the Ledger is wiped the removal of
the keys will be forgotten but the original PUTs would still remain.
The safest thing maybe to have rule that tombstones are never deleted
from the Inker's Journal - and accept the build-up of garbage. Or there
could be an addition to the compaction process that checks back through
all the inker files to check that the Key of a tombstone is not present
in the past, before it is removed in the compaction.
There was a test that failed to close down a bookie and that caused some
issues. The issues are double-reoslved, the close down was tidied as
well as the forgotten close being added back in.
There is some generla tidy around in anticipation of TTL support.
