Import wiredtiger-wiredtiger-2.7.0-505-g7fea169.tar.gz from wiredtiger branch mongodb-3.4

ref: 44463c5..7fea169

WT-2355       Fix minor scratch buffer usage in logging.
WT-2348       xargs -P isn't portable
WT-2347       Java: schema format edge cases
WT-2344       OS X compiler warning
WT-2342       Enhance wtperf to support background create and drop operations
WT-2340       Add logging guarantee assertions, whitespace
WT-2339       format post-rebalance verify failure (stress run #11586)
WT-2338       Disable using pre-allocated log files when backup cursor is open
WT-2335       NULL pointer crash in config_check_search with invalid configuration string
WT-2333       Add a flag so drop doesn't block
WT-2332       Bug in logging write-no-sync mode
WT-2331       Checking of search() result for reference cursors before join()
WT-2328       schema drop does direct unlink, it should use a block manager interface.
WT-2326       Change WTPERF to use new memory allocation functions instead of the standard
WT-2321       WT-2321: race between eviction and worker threads on the eviction queue
WT-2320       Only check copyright when cutting releases
WT-2316       stress test failure: WT_CURSOR.prev out-of-order returns
WT-2314       page-swap error handling is inconsistent
WT-2313       sweep-server: conn_dhandle.c, 610: dhandle != conn->cache->evict_file_next
WT-2312       re-creating a deleted column-store page can corrupt the in-memory tree
WT-2308       custom extractor for ref_cursors in join cursor
WT-2305       Fix coverity scan issues on 23/12/2015
WT-2296       New log algorithm needs improving for sync/flush settings
WT-2295       WT_SESSION.create does a full-scan of the main table
WT-2287       WT_SESSION.rebalance
WT-2275       broken DB after application crash
WT-2267       Improve wtperf throttling implementation to provide steady load
WT-2247       variable-length column-store in-memory page splits
WT-2242       WiredTiger treats dead trees the same as other trees in eviction
WT-2142       Connection cleanup in Python tests
WT-2073       metadata cleanups
WT-1801       Add a directory sync after rollback of a WT_SESSION::rename operation
WT-1517       schema format edge cases
SERVER-22064  Coverity analysis defect 77699: Unchecked return value
SERVER-21619  sys-perf: WT crash during core_workloads_WT execution

1 files changed, 41 insertions, 0 deletions

diff --git a/src/third_party/wiredtiger/src/docs/shared-cache.dox b/src/third_party/wiredtiger/src/docs/shared-cache.dox
new file mode 100644
index 00000000000..95422caabda
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+/*! @m_page{{c,java},shared_cache,Per-process shared caches}
+
+WiredTiger supports sharing a single cache among multiple databases within
+a process.
+
+An application configures a shared cache by specifying a shared_cache name
+to the ::wiredtiger_open function. Applications can optionally
+set a minimum amount of cache any connection in the pool will be assigned
+and the granularity at which the cache pool is redistributed among
+connections - called the chunk size.
+
+The shared cache implementation assigns a certain amount of cache to each
+participating database. Each database manages its allocated cache
+as it would when not using a shared cache - thus databases using a shared
+cache can have different eviction policies. There is a thread that monitors
+the cache usage of each database and redistributes the cache among
+participants according to where it is most likely to improve performance.
+The cache is redistributed in chunks which are of a configurable size. Once
+a database has had a chunk of cache added or removed it will be given
+time to start effectively using that cache before it is considered for further
+adjustment. If a small chunk size is configured it will take longer for the
+shared cache to adjust to changes in participants. Reallocation of resources
+happens periodically and whenever a database joins the shared cache.
+
+The reallocation of resources is determined by comparing the amount of eviction
+activity in a particular database to that of the other participating databases.
+
+When a database is opened it will be allocated the amount of cache configured
+as the shared cache minimum, regardless of whether the cache pool is currently
+fully utilized. Other databases will have their assigned cache size
+reduced so the total cache size used will return within the bounds - there
+may be a period when the actual usage exceeds the configured maximum.
+This is especially likely if many databases join the shared cache in a short
+period. When a database is closed any resources it is using are distributed
+among the other databases.
+
+WiredTiger shared cache tuning options can be configured when first opening a
+database via ::wiredtiger_open or changed after open using the
+WT_CONNECTION::reconfigure method.
+
+ */