Quick seed 21691 used to generate duplicate keys,
which caused some Puts of values to overwrite other values,
causing spurious test failures.
Fixes#629.
The existing append-based implementation left a hanging reference to
the last tx.
For example, if db.txs was:
[]*Tx{0x1, 0x2, 0x3, 0x4, 0x5}
and we removed the second element, db.txs would now be:
[]*Tx{0x1, 0x3, 0x4, 0x5, 0x5}[:4]
The garbage collector cannot reclaim anything anywhere in a slice,
even pointers between its len and cap, because the len can always
be extended up to the cap.
This hanging reference to the Tx could last indefinitely,
and since the Tx has a reference to user-provided functions,
which could be closures, this bug could prevent arbitrary
amounts of user garbage from being collected.
Since db.txs is unordered anyway, switch to a simpler--and O(1) instead
of O(n)--implementation. Swap the last element into the spot to be
deleted, nil out the original last element, and shrink the slice.
Using a large (50gb) database with a read-write-delete heavy load,
nearly 100% of allocated space came from freelists.
1/3 came from freelist.release, 1/3 from freelist.write,
and 1/3 came from tx.allocate to make space for freelist.write.
In the case of freelist.write, the newly allocated giant slice gets
copied to the space prepared by tx.allocate and then discarded.
To avoid this, add func mergepgids that accepts a destination slice,
and use it in freelist.write.
This has a mild negative impact on the existing benchmarks,
but cuts allocated space in my real world db by over 30%.
name old time/op new time/op delta
_FreelistRelease10K-8 18.7µs ±10% 18.2µs ± 4% ~ (p=0.548 n=5+5)
_FreelistRelease100K-8 233µs ± 5% 258µs ±20% ~ (p=0.151 n=5+5)
_FreelistRelease1000K-8 3.34ms ± 8% 3.13ms ± 8% ~ (p=0.151 n=5+5)
_FreelistRelease10000K-8 32.3ms ± 1% 32.2ms ± 7% ~ (p=0.690 n=5+5)
DBBatchAutomatic-8 2.18ms ± 3% 2.19ms ± 4% ~ (p=0.421 n=5+5)
DBBatchSingle-8 140ms ± 6% 140ms ± 4% ~ (p=0.841 n=5+5)
DBBatchManual10x100-8 4.41ms ± 2% 4.37ms ± 3% ~ (p=0.548 n=5+5)
name old alloc/op new alloc/op delta
_FreelistRelease10K-8 82.5kB ± 0% 82.5kB ± 0% ~ (all samples are equal)
_FreelistRelease100K-8 805kB ± 0% 805kB ± 0% ~ (all samples are equal)
_FreelistRelease1000K-8 8.05MB ± 0% 8.05MB ± 0% ~ (all samples are equal)
_FreelistRelease10000K-8 80.4MB ± 0% 80.4MB ± 0% ~ (p=1.000 n=5+5)
DBBatchAutomatic-8 384kB ± 0% 384kB ± 0% ~ (p=0.095 n=5+5)
DBBatchSingle-8 17.2MB ± 1% 17.2MB ± 1% ~ (p=0.310 n=5+5)
DBBatchManual10x100-8 908kB ± 0% 902kB ± 1% ~ (p=0.730 n=4+5)
name old allocs/op new allocs/op delta
_FreelistRelease10K-8 5.00 ± 0% 5.00 ± 0% ~ (all samples are equal)
_FreelistRelease100K-8 5.00 ± 0% 5.00 ± 0% ~ (all samples are equal)
_FreelistRelease1000K-8 5.00 ± 0% 5.00 ± 0% ~ (all samples are equal)
_FreelistRelease10000K-8 5.00 ± 0% 5.00 ± 0% ~ (all samples are equal)
DBBatchAutomatic-8 10.2k ± 0% 10.2k ± 0% +0.07% (p=0.032 n=5+5)
DBBatchSingle-8 58.6k ± 0% 59.6k ± 0% +1.70% (p=0.008 n=5+5)
DBBatchManual10x100-8 6.02k ± 0% 6.03k ± 0% +0.17% (p=0.029 n=4+4)
The subtraction for `TxN` was previously transposed which caused
the result to be a negative number. This change alters the order
to return the correct (positive) result.
Marc
Ben Johnson
Chyroc
Tommi Virtanen
Steve Manuel
Sebastian
Josh Bleecher Snyder
Bjørn Erik Pedersen
Tim Shannon
Ben Aldrich
John C. Vernaleo
tbe
nick
Jared Folkins
Hasit Mistry
Denis Andrejew
Janoš Guljaš
Roman Naumann