Timeline for How to verify disk hit by a query
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 28, 2016 at 8:29 | comment | added | jjanes | Local buffers hold data for explicitly created temporary objects, like 'CREATE TEMP TABLE...'. These have a life span of a session or a transaction. Temp buffers hold data for implicit operations like sorts, hash tables, etc that don't fit in memory. They only last for a single statement. | |
| Apr 27, 2016 at 6:33 | comment | added | Gowtham Kumar | One more question on this , am going through the documentation and got to know there are shared hit , local hit and temp hit . What is the difference among them ? what am interpreting here is 'Shared hit is on actual table' and local hit means on temporary table (virtual table) which got created because of execution of query . How does temp hit differs from local hit . please find the below doc which am referring : postgresql.org/docs/9.4/static/sql-explain.html | |
| Feb 12, 2016 at 16:37 | comment | added | jjanes | You can't reliably interpret these numbers as finely as you trying to do. Often one process will find a bit of dirty data that someone else left behind which is inconveniencing it, and will write it out. | |
| Feb 12, 2016 at 9:57 | comment | added | Gowtham Kumar | To be more specific 'am seeing difference in the values of in/out for eg: 2016-02-12 01:54:21 PST LOG: statement: insert into test_sql_source values (1); is causing 0/32 [1712/528] filesystem blocks in/out and if i run the same query again (insert statement ) > 2016-02-12 01:54:21 PST STATEMENT: insert into test_sql_source values (1); is causing 0/16 [1712/544] filesystem blocks in/out | |
| Feb 12, 2016 at 9:52 | comment | added | Gowtham Kumar | Hi , I have a 'DDL' statement which is causing some file system in/out below are the logs: 2016-02-12 01:22:53 PST LOG: statement: create table test_sql_source (col1 numeric ); 2016-02-12 01:22:53 PST LOG: QUERY STATISTICS 2016-02-12 01:22:53 PST DETAIL: ! system usage stats: ! 0.005942 elapsed 0.001000 user 0.002000 system sec ! [0.017997 user 0.028995 sys total] ! 16/80 [1712/496] filesystem blocks in/out I am more interested to know about 16/80 what exactly this "in" value and out value means ? in the previous logs because in/out values are 0/0 , i did not understand it exactly. | |
| Feb 8, 2016 at 8:56 | comment | added | Gowtham Kumar | ok , thanks for clarification . I got what am looking for . 0/0 is my query statistics and [3280/26440] filesystem blocks in/out indicates session level statistics . | |
| Feb 5, 2016 at 16:12 | comment | added | jjanes | Yes, those are for the backend (the process you are connected to) for its entire lifetime, which is the same lifetime as your session. Your specific query seems to have no reads or writes, "0/0". Everything it needed was already in memory. BTW, on my Linux machine, a block seems to be 512 bytes. | |
| Feb 5, 2016 at 2:08 | comment | added | Gowtham Kumar | Hi , Thanks for your answer. But , could you please more specific i.e, when you said ," The numbers in square brackets are total for the session so far" are you saying that [3280/26440] filesystem blocks in/out those values are for session level ? if so, could you please help me to figure out file system block reads for above select query ? | |
| Feb 4, 2016 at 18:06 | history | answered | jjanes | CC BY-SA 3.0 |