Wired Tiger in Mongo

Wired tiger is a pluggable storage engine with following features:
* Document level locking
* Compression
* Fulfills some pitfalls of MMAPv1
* Performance gain

We can specify the specific storage engine on which we want to run the mongo instance as below

mongod  --storageEngine wiredTiger

Data files of a wired tiger Storage Engine:

-rw—––. 1 mongod mongod   21 Sep 15  2010 WiredTiger.lock
-rw—––. 1 mongod mongod   45 Sep 15  2010 WiredTiger
-rw—––. 1 mongod mongod  114 Sep 15  2010 storage.bson
-rw—––. 1 mongod mongod 4.0K Mar 20 07:37 WiredTigerLAS.wt
-rw—––. 1 mongod mongod    5 Mar 20 07:37 mongod.lock
-rw—––. 1 mongod mongod  32K Mar 20 07:38 index-3–5338574939802031263.wt
-rw—––. 1 mongod mongod  32K Mar 20 07:38 collection-2–5338574939802031263.wt
drwx——. 2 mongod mongod 4.0K Mar 20 07:38 journal
-rw—––. 1 mongod mongod  32K Mar 20 07:42 index-8–5338574939802031263.wt
-rw—––. 1 mongod mongod  36K Mar 20 07:43 collection-7–5338574939802031263.wt
-rw—––. 1 mongod mongod  16K Mar 20 08:05 index-1–1414695316089644899.wt
-rw—––. 1 mongod mongod  16K Mar 20 08:05 collection-0–1414695316089644899.wt
-rw—––. 1 mongod mongod  36K Mar 20 08:05 _mdb_catalog.wt
-rw—––. 1 mongod mongod  32K Mar 20 23:27 index-1–5338574939802031263.wt
-rw—––. 1 mongod mongod  32K Mar 20 23:27 collection-0–5338574939802031263.wt
-rw—––. 1 mongod mongod  24K Mar 21 01:21 index-5–5338574939802031263.wt
-rw—––. 1 mongod mongod  24K Mar 21 01:21 collection-4–5338574939802031263.wt
-rw—––. 1 mongod mongod  36K Mar 21 01:22 sizeStorer.wt
-rw—––. 1 mongod mongod  12K Mar 21 01:22 index-6–5338574939802031263.wt
-rw—––. 1 mongod mongod  68K Mar 21 01:22 WiredTiger.wt
-rw—––. 1 mongod mongod 1.1K Mar 21 01:22 WiredTiger.turtle
drwx——. 2 mongod mongod 4.0K Mar 21 04:21 diagnostic.data

Wired Tiger Internals

* Stores data in btree

* Writes are initially seperate,incorporated later

* two caches are used - WT cache which is by default set as half of RAM and FS cache.

Two caches are used before writing to disk to improve performance with a 60s checkpoint.

At cache level, wired tiger compressed the data.

The compressions used by WT are :

* Snappy - (default) - This is a fast compression mode

* zlib - this has the capability of compressing more

*none