IndexedDB: Enabled the LevelDB Bloom filter

IndexedDB: Enabled the LevelDB Bloom filter

Enabling a LevelDB feature to improve performance.

BUG=409520
Committed: https://crrev.com/8aec45ee2c9b7c74ea4b317bf756db660ad7ff27
Cr-Commit-Position: refs/heads/master@{#294673}

[cmumford, 2014-09-11 23:55:47]

cmumford@chromium.org changed reviewers:
+ dgrogan@chromium.org, jsbell@chromium.org

[cmumford, 2014-09-11 23:55:48]

Two caveats to this change:

1. Existing databases won't see any improvement until new table files are
created.

2. LevelDB's comment on the bloom filter states:

Note: if you are using a custom comparator that ignores some parts of the keys
being compared, you must not use NewBloomFilterPolicy() and must provide your
own FilterPolicy that also ignores the corresponding parts of the keys.  For
example, if the comparator ignores trailing spaces, it would be incorrect to use
a FilterPolicy (like NewBloomFilterPolicy) that does not ignore trailing spaces
in keys.

I believe that IndexedDB's comparator does use all bits, but wanted to point
this out for your consideration.

[jsbell, 2014-09-12 00:14:44]

Agreed re: comparator. So far as I recall and can tell by looking in
leveldb_coding we never skip over bits while doing regular comparisons. (We pass
a flag into Compare for certain index-key operations to short-circuit the
comparison, but that's not used for the leveldb comparator itself).

Can we add a note about this bloom filter restriction to the leveldb_coding
comment block?

lgtm but suggestion for tweaking the pointers....

https://codereview.chromium.org/562333005/diff/20001/content/browser/indexed_...
File content/browser/indexed_db/leveldb/leveldb_database.cc (right):

https://codereview.chromium.org/562333005/diff/20001/content/browser/indexed_...
content/browser/indexed_db/leveldb/leveldb_database.cc:98: const
leveldb::FilterPolicy** filter_policy) {
How about passing a scoped_ptr<leveldb::FilterPolicy>* instead?

Then allocate/assign to it immediately, reset it if the open fails, to avoid any
time in this function where it's not held on to?

[dgrogan, 2014-09-12 01:18:35]

Don't wait on me to submit this, I don't know anything about leveldb's bloom
filter implementation. lgtm as far as I am concerned.

[cmumford, 2014-09-12 20:58:50]

The CQ bit was checked by cmumford@chromium.org

[commit-bot: I haz the power, 2014-09-12 20:59:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/562333005/60001

[commit-bot: I haz the power, 2014-09-12 22:02:38]

Committed patchset #4 (id:60001) as 6028b6f6eb945f900544e6a697103254569a38de

[commit-bot: I haz the power, 2014-09-12 22:05:47]

Patchset 4 (id:??) landed as
https://crrev.com/8aec45ee2c9b7c74ea4b317bf756db660ad7ff27
Cr-Commit-Position: refs/heads/master@{#294673}