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Diffstat (limited to 'src/third_party/wiredtiger/src/docs/shared-cache.dox')
| -rw-r--r-- | src/third_party/wiredtiger/src/docs/shared-cache.dox | 41 |
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 --- /dev/null +++ b/src/third_party/wiredtiger/src/docs/shared-cache.dox @@ -0,0 +1,41 @@ +/*! @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. + + */ |