Thread

1. BUG #19103: Canceled INSERT statement can still influence the performance of subsequent SELECT statement

   PG Bug reporting form <noreply@postgresql.org> — 2025-11-04T12:08:00Z

   The following bug has been logged on the website:
   
   Bug reference:      19103
   Logged by:          Jinhui Lai
   Email address:      jinhui.lai@qq.com
   PostgreSQL version: 18.0
   Operating system:   ubuntu 22.04
   Description:        
   
   Dear PG developers:
   
   Thanks for reading my report. Here, I find a performance issue.  I have
   found a performance issue where a canceled INSERT statement appears to
   negatively impact the performance of subsequent SELECT queries.
   
   Steps to Reproduce:
   
   \timing on
   CREATE TABLE t0(c0 INT8);
   INSERT INTO t1 VALUES(1);
   CREATE TABLE t1(c1 INT8);
   INSERT INTO t1 SELECT * FROM generate_series(1, 100000000);
   ^CCancel request sent
   ERROR:  canceling statement due to user request
   Time: 50685.063 ms (00:50.685)
   
   SELECT COUNT(*) FROM t0;
    count
   -------
        0
   (1 row)
   Time: 1.264 ms
   
   SELECT COUNT(*) FROM t1;
    count
   -------
        0
   (1 row)
   Time: 3466.933 ms (00:03.467)
   
   This performance degradation could affect systems where large batch
   operations are frequently started and canceled, potentially impacting
   overall database responsiveness.
   
   Thank you for investigating this issue.
   
   Best regards,
   Jinhui Lai
   
   

2. Re: BUG #19103: Canceled INSERT statement can still influence the performance of subsequent SELECT statement

   David G. Johnston <david.g.johnston@gmail.com> — 2025-11-04T13:26:01Z

   On Tuesday, November 4, 2025, PG Bug reporting form <noreply@postgresql.org>
   wrote:
   
   > The following bug has been logged on the website:
   >
   > Bug reference:      19103
   > Logged by:          Jinhui Lai
   > Email address:      jinhui.lai@qq.com
   > PostgreSQL version: 18.0
   > Operating system:   ubuntu 22.04
   > Description:
   >
   > Dear PG developers:
   >
   > Thanks for reading my report. Here, I find a performance issue.  I have
   > found a performance issue where a canceled INSERT statement appears to
   > negatively impact the performance of subsequent SELECT queries.
   
   
   This doesn’t feel like a bug.  Processing deleted rows is expensive and
   some of that work happens during selects if/when those dead rows are
   encountered.
   
   
   > This performance degradation could affect systems where large batch
   > operations are frequently started and canceled, potentially impacting
   > overall database responsiveness.
   >
   
   Temporary tables are nice for this kind of flow.  Don’t touch production
   tables until you know what you are going to insert is going to stick.
   
   David J.
   

3. Re: BUG #19103: Canceled INSERT statement can still influence the performance of subsequent SELECT statement

   Tom Lane <tgl@sss.pgh.pa.us> — 2025-11-04T14:55:28Z

   "David G. Johnston" <david.g.johnston@gmail.com> writes:
   > On Tuesday, November 4, 2025, PG Bug reporting form <noreply@postgresql.org>
   > wrote:
   >> Thanks for reading my report. Here, I find a performance issue.  I have
   >> found a performance issue where a canceled INSERT statement appears to
   >> negatively impact the performance of subsequent SELECT queries.
   
   > This doesn’t feel like a bug.
   
   It is not.  The reason ROLLBACK is essentially free in Postgres
   is that some of the ensuing cleanup work gets done during
   subsequent table accesses.  Some other DBMSes do that differently,
   but that's our choice and we're not likely to revisit it.
   
   > Temporary tables are nice for this kind of flow.  Don’t touch production
   > tables until you know what you are going to insert is going to stick.
   
   Yeah.  Frequently rolling back large data modifications is a
   performance anti-pattern no matter what the underlying implementation
   does.
   
   			regards, tom lane
   
   
   
   

4. Re: BUG #19103: Canceled INSERT statement can still influence the performance of subsequent SELECT statement

   Álvaro Herrera <alvherre@kurilemu.de> — 2025-11-07T15:51:54Z

   On 2025-Nov-04, Tom Lane wrote:
   
   > It is not.  The reason ROLLBACK is essentially free in Postgres
   > is that some of the ensuing cleanup work gets done during
   > subsequent table accesses.  Some other DBMSes do that differently,
   > but that's our choice and we're not likely to revisit it.
   
   At least, it's the choice we have made in heapam.  It's possible to make
   different choices for other table AMs -- for instance, I bet OrioleDB
   has made a different choice here, because of its claim that vacuum is
   not needed.
   
   -- 
   Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
   "El hombre nunca sabe de lo que es capaz hasta que lo intenta" (C. Dickens)