Re: [HACKERS] Deadlock with pg_dump?
I have applied a modified version of this patch, attached. I trimmed down the description of log_lock_waits to be more concise, and moved the idea of using this to tune deadlock_timeout to the deadlock_timeout section of the manual. --- Simon Riggs wrote: > On Mon, 2007-02-19 at 19:38 +, Simon Riggs wrote: > > On Tue, 2007-02-13 at 22:19 -0500, Bruce Momjian wrote: > > > Simon Riggs wrote: > > > > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > > > > > Chris Campbell <[EMAIL PROTECTED]> writes: > > > > > > Is there additional logging information I can turn on to get more > > > > > > details? I guess I need to see exactly what locks both processes > > > > > > hold, and what queries they were running when the deadlock > > > > > > occurred? > > > > > > Is that easily done, without turning on logging for *all* > > > > > > statements? > > > > > > > > > > log_min_error_statement = error would at least get you the statements > > > > > reporting the deadlocks, though not what they're conflicting against. > > > > > > > > Yeh, we need a much better locking logger for performance analysis. > > > > > > > > We really need to dump the whole wait-for graph for deadlocks, since > > > > this might be more complex than just two statements involved. Deadlocks > > > > ought to be so infrequent that we can afford the log space to do this - > > > > plus if we did this it would likely lead to fewer deadlocks. > > > > > > > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter > > > > that would allow you to dump the wait-for graph for any data-level locks > > > > that wait too long, rather than just those that deadlock. Many > > > > applications experience heavy locking because of lack of holistic > > > > design. That will also show up the need for other utilities to act > > > > CONCURRENTLY, if possible. > > > > > > Old email, but I don't see how our current output is not good enough? > > > > > > test=> lock a; > > > ERROR: deadlock detected > > > DETAIL: Process 6855 waits for AccessExclusiveLock on relation 16394 of > > > database 16384; blocked by process 6795. > > > Process 6795 waits for AccessExclusiveLock on relation 16396 of database > > > 16384; blocked by process 6855. > > > > This detects deadlocks, but it doesn't detect lock waits. > > > > When I wrote that it was previous experience driving me. Recent client > > experience has highlighted the clear need for this. We had a lock wait > > of 50 hours because of an RI check; thats the kind of thing I'd like to > > show up in the logs somewhere. > > > > Lock wait detection can be used to show up synchronisation points that > > have been inadvertently designed into an application, so its a useful > > tool in investigating performance issues. > > > > I have a patch implementing the logging as agreed with Tom, will post to > > patches later tonight. > > Patch for discussion, includes doc entries at top of patch, so its > fairly clear how it works. > > Output is an INFO message, to allow this to trigger > log_min_error_statement when it generates a message, to allow us to see > the SQL statement that is waiting. This allows it to generate a message > prior to the statement completing, which is important because it may not > ever complete, in some cases, so simply logging a list of pids won't > always tell you what the SQL was that was waiting. > > Other approaches are possible... > > Comments? > > -- > Simon Riggs > EnterpriseDB http://www.enterprisedb.com > [ Attachment, skipping... ] -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + Index: doc/src/sgml/config.sgml === RCS file: /cvsroot/pgsql/doc/src/sgml/config.sgml,v retrieving revision 1.113 diff -c -c -r1.113 config.sgml *** doc/src/sgml/config.sgml 2 Mar 2007 23:37:22 - 1.113 --- doc/src/sgml/config.sgml 3 Mar 2007 18:41:13 - *** *** 2946,2951 --- 2946,2966 + + log_lock_waits (boolean) + +log_lock_waits configuration parameter + + + + Controls whether a log message is produced when a statement waits + longer than to acquire a + lock. This is useful in determining if lock waits are causing + poor performance. The default is off. + + + + log_temp_files (integer) *** *** 3980,3996 This is the amount of time, in milliseconds, to wait on a lock before checking to see if there is a deadlock condition. The check for deadlock is relatively slow, so the server doesn't run ! it every time it waits for a lock. We (optim
Re: [HACKERS] Deadlock with pg_dump?
I will rework this before application to use LOG level. Your patch has been added to the PostgreSQL unapplied patches list at: http://momjian.postgresql.org/cgi-bin/pgpatches It will be applied as soon as one of the PostgreSQL committers reviews and approves it. --- Simon Riggs wrote: > On Mon, 2007-02-19 at 19:38 +, Simon Riggs wrote: > > On Tue, 2007-02-13 at 22:19 -0500, Bruce Momjian wrote: > > > Simon Riggs wrote: > > > > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > > > > > Chris Campbell <[EMAIL PROTECTED]> writes: > > > > > > Is there additional logging information I can turn on to get more > > > > > > details? I guess I need to see exactly what locks both processes > > > > > > hold, and what queries they were running when the deadlock > > > > > > occurred? > > > > > > Is that easily done, without turning on logging for *all* > > > > > > statements? > > > > > > > > > > log_min_error_statement = error would at least get you the statements > > > > > reporting the deadlocks, though not what they're conflicting against. > > > > > > > > Yeh, we need a much better locking logger for performance analysis. > > > > > > > > We really need to dump the whole wait-for graph for deadlocks, since > > > > this might be more complex than just two statements involved. Deadlocks > > > > ought to be so infrequent that we can afford the log space to do this - > > > > plus if we did this it would likely lead to fewer deadlocks. > > > > > > > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter > > > > that would allow you to dump the wait-for graph for any data-level locks > > > > that wait too long, rather than just those that deadlock. Many > > > > applications experience heavy locking because of lack of holistic > > > > design. That will also show up the need for other utilities to act > > > > CONCURRENTLY, if possible. > > > > > > Old email, but I don't see how our current output is not good enough? > > > > > > test=> lock a; > > > ERROR: deadlock detected > > > DETAIL: Process 6855 waits for AccessExclusiveLock on relation 16394 of > > > database 16384; blocked by process 6795. > > > Process 6795 waits for AccessExclusiveLock on relation 16396 of database > > > 16384; blocked by process 6855. > > > > This detects deadlocks, but it doesn't detect lock waits. > > > > When I wrote that it was previous experience driving me. Recent client > > experience has highlighted the clear need for this. We had a lock wait > > of 50 hours because of an RI check; thats the kind of thing I'd like to > > show up in the logs somewhere. > > > > Lock wait detection can be used to show up synchronisation points that > > have been inadvertently designed into an application, so its a useful > > tool in investigating performance issues. > > > > I have a patch implementing the logging as agreed with Tom, will post to > > patches later tonight. > > Patch for discussion, includes doc entries at top of patch, so its > fairly clear how it works. > > Output is an INFO message, to allow this to trigger > log_min_error_statement when it generates a message, to allow us to see > the SQL statement that is waiting. This allows it to generate a message > prior to the statement completing, which is important because it may not > ever complete, in some cases, so simply logging a list of pids won't > always tell you what the SQL was that was waiting. > > Other approaches are possible... > > Comments? > > -- > Simon Riggs > EnterpriseDB http://www.enterprisedb.com > [ Attachment, skipping... ] -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [PATCHES] [HACKERS] Deadlock with pg_dump?
Bruce Momjian <[EMAIL PROTECTED]> writes: > This is not the first GUC that has needed this. Exactly. I think that we simply made a mistake in the initial implementation of log_min_error_statement: we failed to think about whether it should use client or server priority ordering, and the easy-to-code behavior was the wrong one. regards, tom lane ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PATCHES] [HACKERS] Deadlock with pg_dump?
Simon Riggs wrote: > On Mon, 2007-02-26 at 13:34 -0500, Bruce Momjian wrote: > > > I am a little concerned about a log_* setting that is INFO. I understand > > why you used INFO (for log_min_error_messages), but INFO is inconsistent > > with the log* prefix, and by default INFO doesn't appear in the log > > file. > > Yeh, LOG would be most appropriate, but thats not possible. > > log_min_messages allows only DEBUG5, DEBUG4, DEBUG3, DEBUG2, DEBUG1, > INFO, NOTICE and WARNING for non-error states. > > Possibly DEBUG1? This highlights a problem we have often had with LOG output where we also want the query. I think there are two possible approaches. First, we could add a new bitmap value like LOG_STATEMENT to ereport when we want the statement with the log line: ereport (LOG | LOG_STATEMENT, ...) (or a new LOG_WITH_STATEMENT log level) and a new GUC like "log_include_statement" that would control the output of statements for certain GUC parameters, and we document with GUC values it controls. A simpler idea would be to unconditionally include the query in the errdetail() of the actual LOG ereport. This is not the first GUC that has needed this. We had this issue with "log_temp_files", which we just added, and the only suggested solution was to use log_statement = 'all'. Either of these ideas above would be useful for this as well. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [HACKERS] Deadlock with pg_dump?
On Mon, 2007-02-26 at 14:52 -0500, Tom Lane wrote: > "Simon Riggs" <[EMAIL PROTECTED]> writes: > > On Mon, 2007-02-26 at 14:28 -0500, Tom Lane wrote: > >> "Simon Riggs" <[EMAIL PROTECTED]> writes: > >>> The idea of the patch is that it generates a log message which then > >>> invokes log_min_error_statement so that the SQL statement is displayed. > >>> LOG is not on the list of options there, otherwise I would use it. > >> > >> As I said, you don't understand how the logging priority control works. > >> LOG *is* the appropriate level for stuff intended to go to the server log. > > > Please look at the definition of log_min_error_statement, so you > > understand where I'm coming from. > > I *have* read the definition of log_min_error_statement. (The SGML docs > are wrong btw, as a quick look at the code shows that LOG is an accepted > value.) OK, I should have looked passed the manual. > The real issue here is that send_message_to_server_log just does > > if (edata->elevel >= log_min_error_statement && debug_query_string != > NULL) > > to determine whether to log the statement, whereas arguably it should be > using a test like is_log_level_output --- that is, the priority ordering > for log_min_error_statement should be like log_min_messages not like > client_min_messages. We've discussed that before in another thread, but > it looks like nothing's been done yet. Hopefully not with me? Don't remember that. > In any case, if you're unhappy > with the code's choice of whether to emit the STATEMENT part of a log > message, some changes here are what's indicated, not bizarre choices of > elevel for individual messages. Well, I would have chosen LOG if I thought it was available. I'll do some more to the patch. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Deadlock with pg_dump?
"Simon Riggs" <[EMAIL PROTECTED]> writes: > On Mon, 2007-02-26 at 14:28 -0500, Tom Lane wrote: >> "Simon Riggs" <[EMAIL PROTECTED]> writes: >>> The idea of the patch is that it generates a log message which then >>> invokes log_min_error_statement so that the SQL statement is displayed. >>> LOG is not on the list of options there, otherwise I would use it. >> >> As I said, you don't understand how the logging priority control works. >> LOG *is* the appropriate level for stuff intended to go to the server log. > Please look at the definition of log_min_error_statement, so you > understand where I'm coming from. I *have* read the definition of log_min_error_statement. (The SGML docs are wrong btw, as a quick look at the code shows that LOG is an accepted value.) The real issue here is that send_message_to_server_log just does if (edata->elevel >= log_min_error_statement && debug_query_string != NULL) to determine whether to log the statement, whereas arguably it should be using a test like is_log_level_output --- that is, the priority ordering for log_min_error_statement should be like log_min_messages not like client_min_messages. We've discussed that before in another thread, but it looks like nothing's been done yet. In any case, if you're unhappy with the code's choice of whether to emit the STATEMENT part of a log message, some changes here are what's indicated, not bizarre choices of elevel for individual messages. regards, tom lane ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [HACKERS] Deadlock with pg_dump?
On Mon, 2007-02-26 at 14:28 -0500, Tom Lane wrote: > "Simon Riggs" <[EMAIL PROTECTED]> writes: > > The idea of the patch is that it generates a log message which then > > invokes log_min_error_statement so that the SQL statement is displayed. > > LOG is not on the list of options there, otherwise I would use it. > > As I said, you don't understand how the logging priority control works. > LOG *is* the appropriate level for stuff intended to go to the server log. Please look at the definition of log_min_error_statement, so you understand where I'm coming from. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] Deadlock with pg_dump?
"Simon Riggs" <[EMAIL PROTECTED]> writes: > The idea of the patch is that it generates a log message which then > invokes log_min_error_statement so that the SQL statement is displayed. > LOG is not on the list of options there, otherwise I would use it. As I said, you don't understand how the logging priority control works. LOG *is* the appropriate level for stuff intended to go to the server log. regards, tom lane ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [HACKERS] Deadlock with pg_dump?
On Mon, 2007-02-26 at 14:11 -0500, Tom Lane wrote: > "Simon Riggs" <[EMAIL PROTECTED]> writes: > > Yeh, LOG would be most appropriate, but thats not possible. > > You have not given any good reason for that. The idea of the patch is that it generates a log message which then invokes log_min_error_statement so that the SQL statement is displayed. LOG is not on the list of options there, otherwise I would use it. The reason for behaving like this is so that a message is generated while the statement is still waiting, rather than at the end. As I mentioned in the submission, you may not like that behaviour; I'm in two minds myself, but I'm trying to get to the stage of having useful information come out of the server when we have long lock waits. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [HACKERS] Deadlock with pg_dump?
"Simon Riggs" <[EMAIL PROTECTED]> writes: > Yeh, LOG would be most appropriate, but thats not possible. You have not given any good reason for that. > log_min_messages allows only DEBUG5, DEBUG4, DEBUG3, DEBUG2, DEBUG1, > INFO, NOTICE and WARNING for non-error states. I don't think you understand quite how the log message priority works... regards, tom lane ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Deadlock with pg_dump?
On Mon, 2007-02-26 at 13:34 -0500, Bruce Momjian wrote: > I am a little concerned about a log_* setting that is INFO. I understand > why you used INFO (for log_min_error_messages), but INFO is inconsistent > with the log* prefix, and by default INFO doesn't appear in the log > file. Yeh, LOG would be most appropriate, but thats not possible. log_min_messages allows only DEBUG5, DEBUG4, DEBUG3, DEBUG2, DEBUG1, INFO, NOTICE and WARNING for non-error states. Possibly DEBUG1? -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Deadlock with pg_dump?
I am a little concerned about a log_* setting that is INFO. I understand why you used INFO (for log_min_error_messages), but INFO is inconsistent with the log* prefix, and by default INFO doesn't appear in the log file. So, by default, the INFO is going to go to the user terminal, and not to the logfile. Ideas? --- Simon Riggs wrote: > On Mon, 2007-02-19 at 19:38 +, Simon Riggs wrote: > > On Tue, 2007-02-13 at 22:19 -0500, Bruce Momjian wrote: > > > Simon Riggs wrote: > > > > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > > > > > Chris Campbell <[EMAIL PROTECTED]> writes: > > > > > > Is there additional logging information I can turn on to get more > > > > > > details? I guess I need to see exactly what locks both processes > > > > > > hold, and what queries they were running when the deadlock > > > > > > occurred? > > > > > > Is that easily done, without turning on logging for *all* > > > > > > statements? > > > > > > > > > > log_min_error_statement = error would at least get you the statements > > > > > reporting the deadlocks, though not what they're conflicting against. > > > > > > > > Yeh, we need a much better locking logger for performance analysis. > > > > > > > > We really need to dump the whole wait-for graph for deadlocks, since > > > > this might be more complex than just two statements involved. Deadlocks > > > > ought to be so infrequent that we can afford the log space to do this - > > > > plus if we did this it would likely lead to fewer deadlocks. > > > > > > > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter > > > > that would allow you to dump the wait-for graph for any data-level locks > > > > that wait too long, rather than just those that deadlock. Many > > > > applications experience heavy locking because of lack of holistic > > > > design. That will also show up the need for other utilities to act > > > > CONCURRENTLY, if possible. > > > > > > Old email, but I don't see how our current output is not good enough? > > > > > > test=> lock a; > > > ERROR: deadlock detected > > > DETAIL: Process 6855 waits for AccessExclusiveLock on relation 16394 of > > > database 16384; blocked by process 6795. > > > Process 6795 waits for AccessExclusiveLock on relation 16396 of database > > > 16384; blocked by process 6855. > > > > This detects deadlocks, but it doesn't detect lock waits. > > > > When I wrote that it was previous experience driving me. Recent client > > experience has highlighted the clear need for this. We had a lock wait > > of 50 hours because of an RI check; thats the kind of thing I'd like to > > show up in the logs somewhere. > > > > Lock wait detection can be used to show up synchronisation points that > > have been inadvertently designed into an application, so its a useful > > tool in investigating performance issues. > > > > I have a patch implementing the logging as agreed with Tom, will post to > > patches later tonight. > > Patch for discussion, includes doc entries at top of patch, so its > fairly clear how it works. > > Output is an INFO message, to allow this to trigger > log_min_error_statement when it generates a message, to allow us to see > the SQL statement that is waiting. This allows it to generate a message > prior to the statement completing, which is important because it may not > ever complete, in some cases, so simply logging a list of pids won't > always tell you what the SQL was that was waiting. > > Other approaches are possible... > > Comments? > > -- > Simon Riggs > EnterpriseDB http://www.enterprisedb.com > [ Attachment, skipping... ] -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Deadlock with pg_dump?
On Mon, 2007-02-19 at 19:38 +, Simon Riggs wrote: > On Tue, 2007-02-13 at 22:19 -0500, Bruce Momjian wrote: > > Simon Riggs wrote: > > > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > > > > Chris Campbell <[EMAIL PROTECTED]> writes: > > > > > Is there additional logging information I can turn on to get more > > > > > details? I guess I need to see exactly what locks both processes > > > > > hold, and what queries they were running when the deadlock occurred? > > > > > Is that easily done, without turning on logging for *all* statements? > > > > > > > > log_min_error_statement = error would at least get you the statements > > > > reporting the deadlocks, though not what they're conflicting against. > > > > > > Yeh, we need a much better locking logger for performance analysis. > > > > > > We really need to dump the whole wait-for graph for deadlocks, since > > > this might be more complex than just two statements involved. Deadlocks > > > ought to be so infrequent that we can afford the log space to do this - > > > plus if we did this it would likely lead to fewer deadlocks. > > > > > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter > > > that would allow you to dump the wait-for graph for any data-level locks > > > that wait too long, rather than just those that deadlock. Many > > > applications experience heavy locking because of lack of holistic > > > design. That will also show up the need for other utilities to act > > > CONCURRENTLY, if possible. > > > > Old email, but I don't see how our current output is not good enough? > > > > test=> lock a; > > ERROR: deadlock detected > > DETAIL: Process 6855 waits for AccessExclusiveLock on relation 16394 of > > database 16384; blocked by process 6795. > > Process 6795 waits for AccessExclusiveLock on relation 16396 of database > > 16384; blocked by process 6855. > > This detects deadlocks, but it doesn't detect lock waits. > > When I wrote that it was previous experience driving me. Recent client > experience has highlighted the clear need for this. We had a lock wait > of 50 hours because of an RI check; thats the kind of thing I'd like to > show up in the logs somewhere. > > Lock wait detection can be used to show up synchronisation points that > have been inadvertently designed into an application, so its a useful > tool in investigating performance issues. > > I have a patch implementing the logging as agreed with Tom, will post to > patches later tonight. Patch for discussion, includes doc entries at top of patch, so its fairly clear how it works. Output is an INFO message, to allow this to trigger log_min_error_statement when it generates a message, to allow us to see the SQL statement that is waiting. This allows it to generate a message prior to the statement completing, which is important because it may not ever complete, in some cases, so simply logging a list of pids won't always tell you what the SQL was that was waiting. Other approaches are possible... Comments? -- Simon Riggs EnterpriseDB http://www.enterprisedb.com Index: doc/src/sgml/config.sgml === RCS file: /projects/cvsroot/pgsql/doc/src/sgml/config.sgml,v retrieving revision 1.108 diff -c -r1.108 config.sgml *** doc/src/sgml/config.sgml 1 Feb 2007 00:28:16 - 1.108 --- doc/src/sgml/config.sgml 6 Feb 2007 12:31:49 - *** *** 2936,2941 --- 2936,2965 + + log_lock_waits (boolean) + +log_lock_waits configuration parameter + + + + Controls whether log messages are produced when a statement is forced + to wait when trying to acquire locks on database objects. The threshold + time is the value of the parameter. + The log messages generated are intended for use during specific + investigations into application performance issues and subsequent tuning. + It is designed for use in conjunction with log_min_error_statement. + Log messages indicating long lock waits might indicate problems with + applications accessing the database or possibly disconnection issues. + If no such problem exist it might indicate that deadlock_timeout + could be set higher. Log messages might also indicate that certain + deadlocks have been avoided. In those cases, decreasing the value of + deadlock_timeout might resolve lock wait situations faster, + thereby reducing contention. By default, this form of logging is off. + + + + Index: src/backend/storage/lmgr/deadlock.c === RCS file: /projects/cvsroot/pgsql/src/backend/storage/lmgr/deadlock.c,v retrieving revision 1.44 diff -c -r1.44 deadlock.c *** src/backend/storage/lmgr/deadlock.c 5 Jan 2007 22:19:38 - 1.44 --- src/backend/storage/lmgr/deadlock.c 6 Feb 2007 12:31:55 - **
Re: [HACKERS] Deadlock with pg_dump?
On Tue, 2007-02-13 at 22:19 -0500, Bruce Momjian wrote: > Simon Riggs wrote: > > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > > > Chris Campbell <[EMAIL PROTECTED]> writes: > > > > Is there additional logging information I can turn on to get more > > > > details? I guess I need to see exactly what locks both processes > > > > hold, and what queries they were running when the deadlock occurred? > > > > Is that easily done, without turning on logging for *all* statements? > > > > > > log_min_error_statement = error would at least get you the statements > > > reporting the deadlocks, though not what they're conflicting against. > > > > Yeh, we need a much better locking logger for performance analysis. > > > > We really need to dump the whole wait-for graph for deadlocks, since > > this might be more complex than just two statements involved. Deadlocks > > ought to be so infrequent that we can afford the log space to do this - > > plus if we did this it would likely lead to fewer deadlocks. > > > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter > > that would allow you to dump the wait-for graph for any data-level locks > > that wait too long, rather than just those that deadlock. Many > > applications experience heavy locking because of lack of holistic > > design. That will also show up the need for other utilities to act > > CONCURRENTLY, if possible. > > Old email, but I don't see how our current output is not good enough? > > test=> lock a; > ERROR: deadlock detected > DETAIL: Process 6855 waits for AccessExclusiveLock on relation 16394 of > database 16384; blocked by process 6795. > Process 6795 waits for AccessExclusiveLock on relation 16396 of database > 16384; blocked by process 6855. This detects deadlocks, but it doesn't detect lock waits. When I wrote that it was previous experience driving me. Recent client experience has highlighted the clear need for this. We had a lock wait of 50 hours because of an RI check; thats the kind of thing I'd like to show up in the logs somewhere. Lock wait detection can be used to show up synchronisation points that have been inadvertently designed into an application, so its a useful tool in investigating performance issues. I have a patch implementing the logging as agreed with Tom, will post to patches later tonight. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Deadlock with pg_dump?
Tom Lane wrote: > Bruce Momjian <[EMAIL PROTECTED]> writes: > > Are we ready to set 'log_min_error_statement = error' by default for > > 8.3? > > We already did that in 8.2. Oh, interesting. Oops again. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Deadlock with pg_dump?
Bruce Momjian <[EMAIL PROTECTED]> writes: > Are we ready to set 'log_min_error_statement = error' by default for > 8.3? We already did that in 8.2. regards, tom lane ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [HACKERS] Deadlock with pg_dump?
Tom Lane wrote: > "Albe Laurenz" <[EMAIL PROTECTED]> writes: > >> [ Memo to hackers: why is it that log_min_error_statement = error > >> isn't the default? ] > > > To avoid spamming the logs with every failed SQL statement? > > Certainly there are people who will turn it off, but that's why it's > configurable. I've had to answer "how do I find out what's causing > error message FOO" often enough that I'm starting to think logging error > statements is a more useful default than not logging 'em ... Are we ready to set 'log_min_error_statement = error' by default for 8.3? -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [HACKERS] Deadlock with pg_dump?
Simon Riggs wrote: > On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > > Chris Campbell <[EMAIL PROTECTED]> writes: > > > Is there additional logging information I can turn on to get more > > > details? I guess I need to see exactly what locks both processes > > > hold, and what queries they were running when the deadlock occurred? > > > Is that easily done, without turning on logging for *all* statements? > > > > log_min_error_statement = error would at least get you the statements > > reporting the deadlocks, though not what they're conflicting against. > > Yeh, we need a much better locking logger for performance analysis. > > We really need to dump the whole wait-for graph for deadlocks, since > this might be more complex than just two statements involved. Deadlocks > ought to be so infrequent that we can afford the log space to do this - > plus if we did this it would likely lead to fewer deadlocks. > > For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter > that would allow you to dump the wait-for graph for any data-level locks > that wait too long, rather than just those that deadlock. Many > applications experience heavy locking because of lack of holistic > design. That will also show up the need for other utilities to act > CONCURRENTLY, if possible. Old email, but I don't see how our current output is not good enough? test=> lock a; ERROR: deadlock detected DETAIL: Process 6855 waits for AccessExclusiveLock on relation 16394 of database 16384; blocked by process 6795. Process 6795 waits for AccessExclusiveLock on relation 16396 of database 16384; blocked by process 6855. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] Deadlock with pg_dump?
On Thu, 2006-10-26 at 18:45 -0400, Tom Lane wrote: > Chris Campbell <[EMAIL PROTECTED]> writes: > > Is there additional logging information I can turn on to get more > > details? I guess I need to see exactly what locks both processes > > hold, and what queries they were running when the deadlock occurred? > > Is that easily done, without turning on logging for *all* statements? > > log_min_error_statement = error would at least get you the statements > reporting the deadlocks, though not what they're conflicting against. Yeh, we need a much better locking logger for performance analysis. We really need to dump the whole wait-for graph for deadlocks, since this might be more complex than just two statements involved. Deadlocks ought to be so infrequent that we can afford the log space to do this - plus if we did this it would likely lead to fewer deadlocks. For 8.3 I'd like to have a log_min_duration_lockwait (secs) parameter that would allow you to dump the wait-for graph for any data-level locks that wait too long, rather than just those that deadlock. Many applications experience heavy locking because of lack of holistic design. That will also show up the need for other utilities to act CONCURRENTLY, if possible. > [ Memo to hackers: why is it that log_min_error_statement = error > isn't the default? ] For production systems where we expect fewer ERRORs, each one is important, so this would be a good default. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Deadlock with pg_dump?
"Albe Laurenz" <[EMAIL PROTECTED]> writes: >> [ Memo to hackers: why is it that log_min_error_statement = error >> isn't the default? ] > To avoid spamming the logs with every failed SQL statement? Certainly there are people who will turn it off, but that's why it's configurable. I've had to answer "how do I find out what's causing error message FOO" often enough that I'm starting to think logging error statements is a more useful default than not logging 'em ... regards, tom lane ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [HACKERS] Deadlock with pg_dump?
Csaba Nagy wrote: > On Fri, 2006-10-27 at 09:23, Albe Laurenz wrote: >> > [ Memo to hackers: why is it that log_min_error_statement = error >> > isn't the default? ] >> >> To avoid spamming the logs with every failed SQL statement? > > And it would be hurting applications where query failure is taken as a > valid path (as inserting first and update if failing)... > Both of these are arguments in favor of being able to alter the level, which would still exist. They are not good arguments for not having error as the default level. cheers andrew ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [HACKERS] Deadlock with pg_dump?
On Fri, 2006-10-27 at 09:23, Albe Laurenz wrote: > > [ Memo to hackers: why is it that log_min_error_statement = error > > isn't the default? ] > > To avoid spamming the logs with every failed SQL statement? And it would be hurting applications where query failure is taken as a valid path (as inserting first and update if failing)... Cheers, Csaba. ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Deadlock with pg_dump?
> [ Memo to hackers: why is it that log_min_error_statement = error > isn't the default? ] To avoid spamming the logs with every failed SQL statement? Yours, Laurenz Albe ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] Deadlock with pg_dump?
On Oct 26, 2006, at 18:45, Tom Lane wrote: log_min_error_statement = error would at least get you the statements reporting the deadlocks, though not what they're conflicting against. Would it be possible (in 8.3, say) to log the conflicting backend's current statement (from pg_stat_activity, perhaps)? I guess the conflicting backend would currently be waiting for a lock, so its current query (before releasing the lock) is the one we want. Thanks! - Chris ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Deadlock with pg_dump?
Tom Lane wrote: > [ Memo to hackers: why is it that log_min_error_statement = error > isn't the default? ] I think it default to panic because it's the way to disable the feature, which was the easiest sell when the feature was introduced. I'm all for lowering it to error. -- Alvaro Herrerahttp://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [HACKERS] Deadlock with pg_dump?
Chris Campbell <[EMAIL PROTECTED]> writes: > Is there additional logging information I can turn on to get more > details? I guess I need to see exactly what locks both processes > hold, and what queries they were running when the deadlock occurred? > Is that easily done, without turning on logging for *all* statements? log_min_error_statement = error would at least get you the statements reporting the deadlocks, though not what they're conflicting against. Still, if you're seeing multiple occurrences per day, that would probably let you build up a good picture of all the involved operations over a couple of days. [ Memo to hackers: why is it that log_min_error_statement = error isn't the default? ] Unless your applications are issuing actual LOCK TABLE commands, it's really hard to see how pg_dump could be involved. It doesn't take anything stronger than AccessShareLock, and shouldn't be holding any tuple-level locks at all. regards, tom lane ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [HACKERS] Deadlock with pg_dump?
On Thu, Oct 26, 2006 at 06:11:59PM -0400, Chris Campbell wrote: > On Oct 26, 2006, at 17:21, Tom Lane wrote: > > >And what was 1171 doing? I really doubt that either of these could > >have > >been pg_dump. > > I know that process 1120 is a Java client (Hibernate) running an > UPDATE query, but I have no idea what 1171 is. I doubt that 1171 was > pg_dump, but when we turn off the pg_dump cron jobs (for 12-ish > hours), the deadlocks go away. We usually see 5 or 6 deadlocks spread > throughout the day. That's not definitive evidence, of course, but > it's certainly curious. I seem to remember something funny about hibernate and locking, though I can't recall any details right now... but searching the archives might provide insight. -- Jim Nasby[EMAIL PROTECTED] EnterpriseDB http://enterprisedb.com 512.569.9461 (cell) ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Deadlock with pg_dump?
On Oct 26, 2006, at 17:21, Tom Lane wrote: And what was 1171 doing? I really doubt that either of these could have been pg_dump. I know that process 1120 is a Java client (Hibernate) running an UPDATE query, but I have no idea what 1171 is. I doubt that 1171 was pg_dump, but when we turn off the pg_dump cron jobs (for 12-ish hours), the deadlocks go away. We usually see 5 or 6 deadlocks spread throughout the day. That's not definitive evidence, of course, but it's certainly curious. Given that you appear to be running 8.1 (tut-tut for not saying), it really shouldn't be a foreign key problem either. I'm betting these are just flat out conflicting updates of the same row(s). Yeah, 8.1.3. Sorry about the omission. Is there additional logging information I can turn on to get more details? I guess I need to see exactly what locks both processes hold, and what queries they were running when the deadlock occurred? Is that easily done, without turning on logging for *all* statements? Thanks! - Chris ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [HACKERS] Deadlock with pg_dump?
Chris Campbell <[EMAIL PROTECTED]> writes: > ERROR: deadlock detected > DETAIL: Process 1120 waits for ShareLock on transaction 5847116; > blocked by process 1171. > Process 1171 waits for ExclusiveLock on tuple (6549,28) of relation > 37637 of database 37574; blocked by process 1120. > Relation 37636 is the users table (schema attached). > Process 1120 was running an UPDATE query and changing a single row in > the users table. And what was 1171 doing? I really doubt that either of these could have been pg_dump. Given that you appear to be running 8.1 (tut-tut for not saying), it really shouldn't be a foreign key problem either. I'm betting these are just flat out conflicting updates of the same row(s). regards, tom lane ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
[HACKERS] Deadlock with pg_dump?
We're getting deadlock error messages in the production database logs during times of inactivity, where the only other thing using the database (we think) is the every-15-minutes pg_dump process. There are still database connections up-and-running from unused Hibernate Java processes, but they Shouldn't Be doing anything (and shouldn't be holding locks, etc). The deadlock error message looks like this: ERROR: deadlock detected DETAIL: Process 1120 waits for ShareLock on transaction 5847116; blocked by process 1171. Process 1171 waits for ExclusiveLock on tuple (6549,28) of relation 37637 of database 37574; blocked by process 1120. Relation 37636 is the users table (schema attached). Process 1120 was running an UPDATE query and changing a single row in the users table. The users table does have foreign keys to 4 other tables. Is it possible that those foreign key constraints acquire locks in a different order than pg_dump (as it's SELECTing from the tables), and it's hitting at *just* the right time to cause a deadlock? I've tried to reproduce it on a test machine by running pgbench (after adding foreign keys to the pgbench tables) and pg_dump in tight loops in two concurrent shell scripts, but no deadlock. Any ideas on how to track this down? Under what conditions does a process acquire a ShareLock on another transaction? Thanks! - Chris Table "public.users" Column | Type | Modifiers --++- user_id | integer| not null default nextval('users_user_id_seq'::regclass) user_last_name | character varying(64) | user_first_name | character varying(64) | user_middle_name | character varying(64) | univ_id | integer| usrtyp_id| integer| user_disabled| boolean| default false customer_id | integer| sysuser_id | integer| user_dob | date | Indexes: "users_pkey" PRIMARY KEY, btree (user_id) Foreign-key constraints: "fk_customer_id" FOREIGN KEY (customer_id) REFERENCES customer(customer_id) ON UPDATE RESTRICT ON DELETE RESTRICT "fk_users_2" FOREIGN KEY (univ_id) REFERENCES universities(univ_id) "fk_users_3" FOREIGN KEY (usrtyp_id) REFERENCES user_type(usrtyp_id) ON UPDATE RESTRICT "system_user_sysuser_id_fkey" FOREIGN KEY (sysuser_id) REFERENCES system_users(sysuser_id) ON UPDATE RESTRICT ON DELETE RESTRICT ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match