diff --git a/source/faq/storage.txt b/source/faq/storage.txt index d1b4b068133..d6e51a19504 100644 --- a/source/faq/storage.txt +++ b/source/faq/storage.txt @@ -101,3 +101,55 @@ active document in memory. For best performance, the majority of your *active* set should fit in RAM. + + +.. todo The following "journal FAQ" content is from the wiki and must be added + to the manual, perhaps on this page. + +.. If I am using replication, can some members use journaling and others + not? + -------------------------------------------------------------------------- + +.. Yes. It is OK to use journaling on some replica set members and not + others. + +.. Can I use the journaling feature to perform safe hot backups? + ------------------------------------------------------------- + +.. Yes, see :doc:`/administration/backups`. + +.. 32 bit nuances? + --------------- + +.. There is extra memory mapped file activity with journaling. This will + further constrain the limited db size of 32 bit builds. Thus, for now + journaling by default is disabled on 32 bit systems. + +.. When did the --journal option change from --dur? + ------------------------------------------------ + +.. In 1.8 the option was renamed to --journal, but the old name is still + accepted for backwards compatibility; please change to --journal if + you are using the old option. + +.. Will the journal replay have problems if entries are incomplete (like + the failure happened in the middle of one)? + ----------------------------------------------------------------------------------------------------------------- + +.. Each journal (group) write is consistent and won't be replayed during + recovery unless it is complete. + +.. How many times is data written to disk when replication and + journaling are both on? + ----------------------------------------------------------------------------------- + +.. In v1.8, for an insert, four times. The object is written to the main + collection and also the oplog collection. Both of those writes are + also journaled as a single mini-transaction in the journal files in + /data/db/journal. + +.. The above applies to collection data and inserts which is the worst + case scenario. Index updates are written to the index and the + journal, but not the oplog, so they should be 2X today not 4X. + Likewise updates with things like $set, $addToSet, $inc, etc. are + compactly logged all around so those are generally small.