Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The answer is <strong>YES</strong>. Prepared statements cut both ways.</p> <p>On the one hand, the query does not have to be re-planned for every execution, saving some overhead. This can make a difference or be hardly noticeable, depending on the complexity of the query.</p> <p>On the other hand, with uneven data distribution, a one-size-fits-all query plan may be a bad choice. Called with particular values another query plan could be (much) better suited.</p> <p>Running the query with parameter values in place can lead to a different query plan. More planning overhead, possibly a (much) better query plan.</p> <p>Also consider <strong><em>unnamed prepared statements</em></strong> like <a href="https://stackoverflow.com/a/9120641/939860">@peufeu provided</a>. Those re-plan the query considering parameters every time - and you still have safe parameter handling.</p> <p>Similar considerations apply to queries inside PL/pgSQL functions, where queries can be treated as prepared statements internally - unless executed dynamically with <code>EXECUTE</code>. I quote the manual on <a href="http://www.postgresql.org/docs/current/interactive/plpgsql-statements.html#PLPGSQL-STATEMENTS-EXECUTING-DYN" rel="nofollow noreferrer">Executing Dynamic Commands</a>:</p> <blockquote> <p>The important difference is that <code>EXECUTE</code> will re-plan the command on each execution, generating a plan that is specific to the current parameter values; whereas PL/pgSQL may otherwise create a generic plan and cache it for re-use. In situations where the best plan depends strongly on the parameter values, it can be helpful to use <code>EXECUTE</code> to positively ensure that a generic plan is not selected.</p> </blockquote> <p>Apart from that, <a href="http://wiki.postgresql.org/wiki/Performance_Optimization" rel="nofollow noreferrer">general guidelines for performance optimization</a> apply.</p>
    singulars
    1. This table or related slice is empty.
    1. POVastly different query run time in application
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USCommunity
    1. USErwin Brandstetter
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POVastly different query run time in application
      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. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COThanks for the answer, Erwin. I think my next test is just to rewrite the query without making it prepared just to see what impact that has on the performance. I figured there was the possibility of a performance hit with prepared_statements but didn't think I'd risk that big a hit.
      singulars
      1. PO
      1. USStAlphonzo
    2. CO@StAlphonzo: It very much depends on your data distribution. If a query can be much faster for certain input parameters you will lose with a general query plan. If input parameters don't make a difference, a pre-planned query will be generally faster.
      singulars
      1. PO
      1. USErwin Brandstetter
    3. COthanks for the updates and the links. In summary, I quickly converted 2 of my most costly queries from being prepare/bind/execute to having the values included in the query. It turns out that in this specific case, prepared_statement is the bottleneck. It's quite likely that our data distribution in this specific table is very clustered on the columns this query looks at.
      singulars
      1. PO
      1. USStAlphonzo
 

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