Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The larger the size of the current primary's oplog, the longer the window of time a replica set member will be able to remain offline without falling too far behind the primary. If it does fall too far behind, it will need a full resync.</p> <p>The field <code>timeDiffHours</code> as returned by <code>db.getReplicationInfo()</code> reports how many hours worth of data the oplog currently has recorded. After the oplog has filled up and starts overwriting old entries, then start to monitor this value. Do so especially under heavy write load (in which the value will decrease). If you then assume it will never drop below N hours, then N is the maximum number of hours that you can tolerate a replica set member being temporarily offline (e.g. for regular maintenance, or to make an offline backup, or in the event of hardware failure) without performing the full resync. The member would then be able to automatically catch up to the primary after coming back online.</p> <p>If you're not comfortable with how low N is, then you should increase the size of the oplog. It completely depends on long your maintenance windows are, or how quickly you or your ops team can respond to disaster scenarios. Be liberal in how much disk space you allocate for it, unless you have a compelling need for that space.</p> <p>I'm assuming here that you're keeping the size of the oplog constant over all replica set members, which is a reasonable thing to do. If not, then plan for the scenario where the replica set member with the smallest oplog gets elected primary.</p> <p>(To answer your other question: similarly to multi-updates, batch inserts are also fanned out into multiple operations in the oplog)</p> <p>Edit: Note that data imports and bulk inserts/updates will write data significantly faster to the oplog than your application might at a typical heavy load. To reiterate: be conservative in your estimation for how much time it will take for the oplog to fill.</p>
    singulars
    1. This table or related slice is empty.
    1. POShould I increase the size of my MongoDB oplog file?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USJ Rassi
    1. USJ Rassi
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POShould I increase the size of my MongoDB oplog file?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThanks for the reply Jason. Also, I am in fact keeping all oplogs the same size.
      singulars
      1. PO
      1. USBrian Hosie
    2. COfyi: to see the max size of the oplog, in the mongo js shell, do `use local` then `db.oplog.rs.stats()` and look for `max`. The `logSizeMB` field above is the actual allocated storage size, not the max. Note that `max` doesn't obey the '[scale factor](http://docs.mongodb.org/manual/reference/database-statistics/#storageSize)' (eg: `db.oplog.rs.stats(1024)` ). This is for mongod version 2.0.4
      singulars
      1. PO
      1. USdrevicko
    3. COChanging oplog size is a **HASSLE**, so create them big enough to begin with using daemon flag "-oplogSize 4096" or similar number. **BEWARE** if you have more than one shard on a box (as I do), the default of oplogsize being 5% of disk size (_NOT_ available space, total size) means 20 shards on a box fills 100% of the space before you've even added any data.
      singulars
      1. PO
      1. USKevin J. Rice
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload