# Disk seeks and stored fields **URL:** \ **Category:** Elasticsearch\ **Created:** [May 31, 2012, 1:20pm UTC](https://discuss.elastic.co/t/disk-seeks-and-stored-fields/7928 "2012-05-31T13:20:25Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Clinton\_Gormley](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Clinton\_Gormley](https://discuss.elastic.co/u/Clinton_Gormley)\ **Post date:** [May 31, 2012, 1:20pm UTC](https://discuss.elastic.co/t/disk-seeks-and-stored-fields/7928/1 "2012-05-31T13:20:25Z")
Jeff Dean from Google gisted some latency numbers, which make for interesting reading. This is why you shouldn't normally store individual fields separately (because each field requires a disk seek): L1 cache reference 0.5 ns Branch mispredict 5 ns L2 cache reference 7 ns Mutex lock/unlock 25 ns Main memory reference 100 ns Compress 1K bytes with Zippy 3,000 ns Send 2K bytes over 1 Gbps network 20,000 ns Read 1 MB sequentially from memory 250,000 ns Round trip within same datacenter 500,000 ns Disk seek 10,000,000 ns Read 1 MB sequentially from disk 20,000,000 ns Send packet CA-\>Netherlands-\>CA 150,000,000 ns By Jeff Dean ([http://research.google.com/people/jeff/](http://research.google.com/people/jeff/)): ---
**Author:** ![Daniel\_Schnell](https://avatars.discourse-cdn.com/v4/letter/d/90ced4/32.png) [@Daniel\_Schnell](https://discuss.elastic.co/u/Daniel_Schnell)\ **Post date:** [May 31, 2012, 7:38pm UTC](https://discuss.elastic.co/t/disk-seeks-and-stored-fields/7928/2 "2012-05-31T19:38:20Z")
Do you mean each field in a separate index ? Am 31.05.2012 um 15:20 schrieb Clinton Gormley: > Jeff Dean from Google gisted some latency numbers, which make for > interesting reading. > > This is why you shouldn't normally store individual fields separately > (because each field requires a disk seek): > > L1 cache reference 0.5 ns > Branch mispredict 5 ns > L2 cache reference 7 ns > Mutex lock/unlock 25 ns > Main memory reference 100 ns > Compress 1K bytes with Zippy 3,000 ns > Send 2K bytes over 1 Gbps network 20,000 ns > Read 1 MB sequentially from memory 250,000 ns > Round trip within same datacenter 500,000 ns > Disk seek 10,000,000 ns > Read 1 MB sequentially from disk 20,000,000 ns > Send packet CA-\>Netherlands-\>CA 150,000,000 ns > > By Jeff Dean ([Jeffrey Dean – Google Research](http://research.google.com/people/jeff/)): ---
**Author:** ![Clinton\_Gormley](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Clinton\_Gormley](https://discuss.elastic.co/u/Clinton_Gormley)\ **Post date:** [June 1, 2012, 11:40am UTC](https://discuss.elastic.co/t/disk-seeks-and-stored-fields/7928/3 "2012-06-01T11:40:26Z")
On Thu, 2012-05-31 at 21:38 +0200, Daniel Schnell wrote: > Do you mean each field in a separate index ? I mean: - by default ES stores your JSON doc in the \_source field, which is set to "stored" - by default, the fields in your JSON doc are set to NOT be "stored" (ie stored as a separate field) - so when ES returns your doc (search or get) it just load the \_source field and returns that, ie a single disk seek Some people think that by storing individual fields, it will be faster than loading the whole JSON doc from the \_source field. What they don't realise is that each stored field requires a disk seek (10ms each seek! ), and that the sum of those seeks far outweighs the cost of just sending the \_source field. In other words, it is almost always a false optimization. clint > Am 31.05.2012 um 15:20 schrieb Clinton Gormley: > > > Jeff Dean from Google gisted some latency numbers, which make for > > interesting reading. > > > > This is why you shouldn't normally store individual fields separately > > (because each field requires a disk seek): > > > > L1 cache reference 0.5 ns > > Branch mispredict 5 ns > > L2 cache reference 7 ns > > Mutex lock/unlock 25 ns > > Main memory reference 100 ns > > Compress 1K bytes with Zippy 3,000 ns > > Send 2K bytes over 1 Gbps network 20,000 ns > > Read 1 MB sequentially from memory 250,000 ns > > Round trip within same datacenter 500,000 ns > > Disk seek 10,000,000 ns > > Read 1 MB sequentially from disk 20,000,000 ns > > Send packet CA-\>Netherlands-\>CA 150,000,000 ns > > > > By Jeff Dean ([Jeffrey Dean – Google Research](http://research.google.com/people/jeff/)): ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 3:26am UTC](https://discuss.elastic.co/t/disk-seeks-and-stored-fields/7928/4 "2017-07-06T03:26:03Z")