During EQC testing it was found that snapshots are still usable even
if the bookie process crashes. This change has snapshots monitor the
bookie and close when the bookie process dies.
head_only mode cna be run with_lookup - but there is no L0 index created in this case.
So the L0 index wasn't returning a potition list and the L0 cache wasn't being checked.
Code now checks every position in the L0 cache, when a lookup is attempted in head_only mode.
The scan_table situation where the query needs to be start inclusive, was consistently getting coverage. It was less likely to get coverage with smaller cache sizes.
It is not clear why this wasn't being triggered before. Perhaps because of the erroneous jitter setting?
Multiple cache sizes now tested to try and make sure the test is always in-line with expectations.
Interetsingly setting max_pencillercachesize to a non-integer merely had the impact of making the penciller cache size infinite.
So a guard added to make sure it is an integer going forward.
Make it easier to discover all the options and the defaults from reaidng the code.
Note default sync option is now none. This doesn't mean this is recommended
ets:next is not StartInclusive - so we shouldn't use ets:next when querying the ledger cache, until it has been confirmed thta a matching key to the StartKey is not present.
This reoslves the intermittently failing unit test which highlighted this (and also makes that intermittent failure a permanent failure by expanding the test cases it covers).
Previously there was no is_empty check, and there was a workaround using binary_bucketlist. But what if there were many buckets - this is a slow seek (using get next key over and over).
Instead have a proper is_empty check.
Originally had disabled the ability to lookup individual values when running in head_only mode. This is a saving of about 11% at PUT time (about 3 microseconds per PUT) on a macbook.
Not sure this saving is sufficient enought to justify the extra work if this is used as an AAE Keystore with Bitcask and LWW (when we need to lookup the current value before adjusting).
So reverted to re-adding support for HEAD requests with these keys.
Initial commit to add head_only mode to leveled. This allows leveled to receive batches of object changes, but where those objects exist only in the Penciller's Ledger (once they have been persisted within the Ledger).
The aim is to reduce significantly the cost of compaction. Also, the objects ar enot directly accessible (they can only be accessed through folds). Again this makes life easier during merging in the LSM trees (as no bloom filters have to be created).
If wast retention period is undefined, then it should be ignored - and no waste retained (rather than retaining waste for 24 hours as at present).
This wasn't working anyway - as reopen reader didn't get the cdb options (which didn't have the waste path on anyway) - so waste would not eb retained if the file had been opened after a stop/start.
