Thread

1. Would SSD improve Index Only Scan performance by a lot?

   Arya F <arya6000@gmail.com> — 2019-10-08T23:37:06Z

   As my table has gotten bigger, it takes longer to get a single row back
   when querying a row by its btree index.
   
   Right now the database is running on a traditional HDD. SSDs have a much
   faster seek time than traditional HDDs.
   
   Would switching to an SSD improve "Index Only Scan" time greatly? by at
   least 3-4 times?
   

2. Sv: Would SSD improve Index Only Scan performance by a lot?

   Andreas Joseph Krogh <andreas@visena.com> — 2019-10-08T23:42:26Z

   På onsdag 09. oktober 2019 kl. 01:37:06, skrev Arya F <arya6000@gmail.com 
   <mailto:arya6000@gmail.com>>: As my table has gotten bigger, it takes longer to 
   get a single row back when querying a row by its btree index. Right now the 
   database is running on a traditional HDD. SSDs have a much faster seek time 
   than traditional HDDs. Would switching to an SSD improve "Index Only Scan" time 
   greatly? by at least 3-4 times? It depends on whether the index is accessed 
   often or not (wrt. caching), and (of course) the size of the index, but yes - 
   "cold access" to the index (or persistent data in general) ismuch faster with 
   SSD. -- Andreas Joseph Krogh CTO / Partner - Visena AS Mobile: +47 909 56 963 
   andreas@visena.com <mailto:andreas@visena.com> www.visena.com 
   <https://www.visena.com>  <https://www.visena.com>

3. Re: Would SSD improve Index Only Scan performance by a lot?

   Rick Otten <rottenwindfish@gmail.com> — 2019-10-09T00:12:48Z

   On Tue, Oct 8, 2019 at 7:37 PM Arya F <arya6000@gmail.com> wrote:
   
   > As my table has gotten bigger, it takes longer to get a single row back
   > when querying a row by its btree index.
   >
   > Right now the database is running on a traditional HDD. SSDs have a much
   > faster seek time than traditional HDDs.
   >
   > Would switching to an SSD improve "Index Only Scan" time greatly? by at
   > least 3-4 times?
   >
   
   *If* your query is disk I/O bound, SSD can help a lot.
   
   If your data is already in memory, or file system cache, and your query is
   bound by CPU or bloated/corrupted indexes, or some query inefficiency, then
   faster disks really won't do anything.
   
   Depending on the data type and size of the data you may be able to help
   your query performance by choosing an index type other than the
   out-of-the-box btree as well (such as a hash or brin index) or maybe even a
   different sort order on the index, or a partial index.
   

4. Re: Would SSD improve Index Only Scan performance by a lot?

   Matthew Hall <mhall@mhcomputing.net> — 2019-10-09T03:17:13Z

   For indexes the SSDs are at least 4X faster but you won't get that to happen unless you fix the planner tunable for the random page fetch cost first. Super important change for SSDs. 
   
   Matthew Hall
   
   > On Oct 8, 2019, at 5:12 PM, Rick Otten <rottenwindfish@gmail.com> wrote:
   > 
   > 
   >> On Tue, Oct 8, 2019 at 7:37 PM Arya F <arya6000@gmail.com> wrote:
   >> As my table has gotten bigger, it takes longer to get a single row back when querying a row by its btree index.
   >> 
   >> Right now the database is running on a traditional HDD. SSDs have a much faster seek time than traditional HDDs. 
   >> 
   >> Would switching to an SSD improve "Index Only Scan" time greatly? by at least 3-4 times?
   > 
   > *If* your query is disk I/O bound, SSD can help a lot.
   > 
   > If your data is already in memory, or file system cache, and your query is bound by CPU or bloated/corrupted indexes, or some query inefficiency, then faster disks really won't do anything.
   > 
   > Depending on the data type and size of the data you may be able to help your query performance by choosing an index type other than the out-of-the-box btree as well (such as a hash or brin index) or maybe even a different sort order on the index, or a partial index.
   > 
   > 
   

5. Re: Would SSD improve Index Only Scan performance by a lot?

   Jeff Janes <jeff.janes@gmail.com> — 2019-10-09T19:54:57Z

   On Tue, Oct 8, 2019 at 7:37 PM Arya F <arya6000@gmail.com> wrote:
   
   > As my table has gotten bigger, it takes longer to get a single row back
   > when querying a row by its btree index.
   >
   >
   Is this in a probabilistic sense, they take longer on average, or has every
   single access gotten slower?  If the increase in size has caused the index
   leaf pages to go from being almost entirely in cache to almost entirely not
   being in cache, the slow down would probably be a lot more 3 to 4 fold.
   But maybe you went from 100% in cache, to 90% in cache and 10% out of cache
   (with a 40 fold slowdown for those ones), coming out to 4 fold slow down on
   average.  If that is the case, maybe you can get the performance back up by
   tweaking some settings, rather than changing hardware.
   
   
   > Right now the database is running on a traditional HDD. SSDs have a much
   > faster seek time than traditional HDDs.
   >
   > Would switching to an SSD improve "Index Only Scan" time greatly? by at
   > least 3-4 times?
   >
   
   If drive access is truly the bottleneck on every single execution, then
   yes, probably far more than 3-4 times.
   
   Cheers,
   
   Jeff