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ntdb's transaction code has an optimization which tdb's doesnt: it
only writes the parts of blocks whose contents have changed. This
means we can actually have a transaction which turns out to need no
recovery region.
This breaks the recovery setup logic, which sets the current recovery
size to 0 if there's no recovery area, and assumes that we'll always
create a new recovery area since the recovery will always need > 0
bytes.
In fact, if we really haven't changed anything, we can skip the
transaction commit altogether: since this happens at least once with
Samba, it's worth doing.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
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Don't expose a libccan.so; it would produce clashes if someone else
does the same thing. Unfortunately, if we just change it from a
SAMBA_LIBRARY to a SAMBA_SUBSYSTEM, it doesn't create a static library
as we'd like, but links all the object files in. This means we get
many duplicates (eg. everyone gets a copy of tally, even though only
ntdb wants it).
So, the solution is twofold:
1) Make the ccan modules separate.
2) Make the ccan modules SAMBA_SUBSYSTEMs not SAMBA_LIBRARYs so we don't
build shared libraries which we can't share.
3) Make the places which uses ccan explicit.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Autobuild-User(master): Rusty Russell <rusty@rustcorp.com.au>
Autobuild-Date(master): Fri Jun 29 06:22:44 CEST 2012 on sn-devel-104
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In particular, this tests that we can store enough records to make the
database expand while we map the given record. We use a global lock for
this, but it could happen in theory with another process.
It also tests the that we can recurse inside ntdb_parse_record().
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Since we have a readlock, any write will grab a write lock: if it happens
to be on the same bucket, we'll fail.
For that reason, enforce read-only so every write operation fails
(even for NTDB_NOLOCK or NTDB_INTERNAL dbs), and document it!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Autobuild-User(master): Jelmer Vernooij <jelmer@samba.org>
Autobuild-Date(master): Thu Jun 21 19:59:57 CEST 2012 on sn-devel-104
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TDB2 started with a top-level hash of 1024 entries, divided into 128
groups of 8 buckets. When a bucket filled, the 8 bucket group
expanded into pointers into 8 new 64-entry hash tables. When these
filled, they expanded in turn, etc.
It's a nice idea to automatically expand the hash tables, but it
doesn't pay off. Remove it for NTDB.
1) It only beats TDB performance when the database is huge and the
TDB hashsize is small. We are about 20% slower on medium-size
databases (1000 to 10000 records), worse on really small ones.
2) Since we're 64 bits, our hash tables are already twice as expensive
as TDB.
3) Since our hash function is good, it means that all groups tend to
fill at the same time, meaning the hash enlarges by a factor of 128
all at once, leading to a very large database at that point.
4) Our efficiency would improve if we enlarged the top level, but
that makes our minimum db size even worse: it's already over 8k,
and jumps to 1M after about 1000 entries!
5) Making the sub group size larger gives a shallower tree, which
performs better, but makes the "hash explosion" problem worse.
6) The code is complicated, having to handle delete and reshuffling
groups of hash buckets, and expansion of buckets.
7) We have to handle the case where all the records somehow end up with
the same hash value, which requires special code to chain records for
that case.
On the other hand, it would be nice if we didn't degrade as badly as
TDB does when the hash chains get long.
This patch removes the hash-growing code, but instead of chaining like
TDB does when a bucket fills, we point the bucket to an array of
record pointers. Since each on-disk NTDB pointer contains some hash
bits from the record (we steal the upper 8 bits of the offset), 99.5%
of the time we don't need to load the record to determine if it
matches. This makes an array of offsets much more cache-friendly than
a linked list.
Here are the times (in ns) for tdb_store of N records, tdb_store of N
records the second time, and a fetch of all N records. I've also
included the final database size and the smbtorture local.[n]tdb_speed
results.
Benchmark details:
1) Compiled with -O2.
2) assert() was disabled in TDB2 and NTDB.
3) The "optimize fetch" patch was applied to NTDB.
10 runs, using tmpfs (otherwise massive swapping as db hits ~30M,
despite plenty of RAM).
Insert Re-ins Fetch Size dbspeed
(nsec) (nsec) (nsec) (Kb) (ops/sec)
TDB (10000 hashsize):
100 records: 3882 3320 1609 53 203204
1000 records: 3651 3281 1571 115 218021
10000 records: 3404 3326 1595 880 202874
100000 records: 4317 3825 2097 8262 126811
1000000 records: 11568 11578 9320 77005 25046
TDB2 (1024 hashsize, expandable):
100 records: 3867 3329 1699 17 187100
1000 records: 4040 3249 1639 154 186255
10000 records: 4143 3300 1695 1226 185110
100000 records: 4481 3425 1800 17848 163483
1000000 records: 4055 3534 1878 106386 160774
NTDB (8192 hashsize)
100 records: 4259 3376 1692 82 190852
1000 records: 3640 3275 1566 130 195106
10000 records: 4337 3438 1614 773 188362
100000 records: 4750 5165 1746 9001 169197
1000000 records: 4897 5180 2341 83838 121901
Analysis:
1) TDB wins on small databases, beating TDB2 by ~15%, NTDB by ~10%.
2) TDB starts to lose when hash chains get 10 long (fetch 10% slower
than TDB2/NTDB).
3) TDB does horribly when hash chains get 100 long (fetch 4x slower
than NTDB, 5x slower than TDB2, insert about 2-3x slower).
4) TDB2 databases are 40% larger than TDB1. NTDB is about 15% larger
than TDB1
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This is designed to allow us to make ntdb_context (and NTDB_DATA returned
from ntdb_fetch) a talloc pointer. But it can also be used for any other
alternate allocator.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Make --valgrind and --valgrind-log options work!
Amitay figured this out!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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We need --error-exitcode=, otherwise valgrind errors don't cause the
test to fail.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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This renames everything from tdb2 to ntdb: importantly, we no longer
use the tdb_ namespace, so you can link against both ntdb and tdb if
you want to.
This also enables building of standalone ntdb by the autobuild script.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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