Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
"Kevin Grittner" writes: > Tom Lane wrote: >> Lastly, I simplified the added code in InitPostgres down to just a >> bare assignment to XactIsoLevel. It doesn't seem worthwhile to >> add all the cycles involved in SetConfigOption(), when we have no >> desire to change the GUC permanently. (I think Kevin's code was >> wrong anyway in that it was using PGC_S_OVERRIDE, which would >> impact the reset state for the GUC.) > Point taken on PGC_S_OVERRIDE. And that probably fixes the issue > that caused me to hold up when I was about ready to pull the trigger > this past weekend. A final round of testing showed a "SET" line on > psql start, which is clearly wrong. I suspected that I needed to go > to a lower level in setting that, but hadn't had a chance to sort > out just what the right path was. In retrospect, just directly > assigning the value seems pretty obvious. Hm, I'm not sure why using SetConfigOption() would result in anything happening client-side. (If this GUC were GUC_REPORT, that would result in a parameter-change report to the client; but it isn't, and anyway that shouldn't cause psql to print "SET".) Might be worth looking closer at what was happening there. >> Kevin, do you want to apply it? You had mentioned wanting some >> practice with back-patches. > I'm getting on a plane to Istanbul in less than 48 hours for the > VLDB conference, and scrambling to tie up loose ends. OK, I've committed it. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
> Tom Lane wrote: > "Kevin Grittner" writes: >> I'll run through my tests again tonight, against your patch, not >> that I expect any problems with it. Unfortunately I can't test >> Windows, as I don't have a build environment for that. > > FWIW, you can approximate Windows close enough for this type of > problem by building with EXEC_BACKEND defined. I usually add the > #define to pg_config.h after configuring, though of course there's > more than one way to do it. It tested out fine both ways. For anybody else wanting to use EXEC_BACKEND for testing -- don't count on --enable-depend to rebuild everything correctly. I used maintainer-clean and it worked. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
"Kevin Grittner" writes: > I'll run through my tests again tonight, against your patch, not > that I expect any problems with it. Unfortunately I can't test > Windows, as I don't have a build environment for that. FWIW, you can approximate Windows close enough for this type of problem by building with EXEC_BACKEND defined. I usually add the #define to pg_config.h after configuring, though of course there's more than one way to do it. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Tom Lane wrote: > I tweaked Kevin's error message to keep the same capitalization as > the existing text for the message in check_XactIsoLevel --- if we > change that it will cause work for the translators, and I don't > think it's enough of an improvement to justify that. That's one of the reasons I agonized over it -- I think the way I left it is a little better and more consistent with other messages, but didn't know whether the difference was worth translator effort. I'm happy to trust your judgment on that. > Lastly, I simplified the added code in InitPostgres down to just a > bare assignment to XactIsoLevel. It doesn't seem worthwhile to > add all the cycles involved in SetConfigOption(), when we have no > desire to change the GUC permanently. (I think Kevin's code was > wrong anyway in that it was using PGC_S_OVERRIDE, which would > impact the reset state for the GUC.) Point taken on PGC_S_OVERRIDE. And that probably fixes the issue that caused me to hold up when I was about ready to pull the trigger this past weekend. A final round of testing showed a "SET" line on psql start, which is clearly wrong. I suspected that I needed to go to a lower level in setting that, but hadn't had a chance to sort out just what the right path was. In retrospect, just directly assigning the value seems pretty obvious. > I think this is ready to go. With your changes, I agree. > Kevin, do you want to apply it? You had mentioned wanting some > practice with back-patches. I'm getting on a plane to Istanbul in less than 48 hours for the VLDB conference, and scrambling to tie up loose ends. I don't want to be under that kind of time-pressure when I back-patch for the first time, for fear of making a mess of things and not being around to clean up the mess; so my first back-patch is probably best left for another time. I'll run through my tests again tonight, against your patch, not that I expect any problems with it. Unfortunately I can't test Windows, as I don't have a build environment for that. Thanks for going over this. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
I wrote:
> I poked around this area a bit. I notice that
> check_transaction_read_only has got the same fundamental error: it
> thinks it can safely consult RecoveryInProgress(), which in general
> it cannot.
After rereading the whole thread I saw that Heikki had already pointed
this out, and come to the same conclusion about how to fix it:
> On reflection I think maybe the best solution is for
> check_transaction_read_only to test IsTransactionState(), and just
> allow the change always if outside a transaction.
Attached is a version of the patch that does it like that. I've checked
that this fixes the problem (as well as Robert's earlier report) in an
EXEC_BACKEND build, which is as close as I can get to the Windows
environment.
I tweaked Kevin's error message to keep the same capitalization as the
existing text for the message in check_XactIsoLevel --- if we change
that it will cause work for the translators, and I don't think it's
enough of an improvement to justify that.
I also back-propagated the use of ERRCODE_FEATURE_NOT_SUPPORTED into
the GUC check hooks. On reflection this seems more appropriate than
ERRCODE_INVALID_PARAMETER_VALUE.
Lastly, I simplified the added code in InitPostgres down to just a
bare assignment to XactIsoLevel. It doesn't seem worthwhile to add
all the cycles involved in SetConfigOption(), when we have no desire
to change the GUC permanently. (I think Kevin's code was wrong anyway
in that it was using PGC_S_OVERRIDE, which would impact the reset
state for the GUC.)
I think this is ready to go. Kevin, do you want to apply it? You
had mentioned wanting some practice with back-patches.
regards, tom lane
diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index 0e9eb3a64f5db66dd2fca68252a597e68defdbf8..5d894ba77f74d02637008deedd4ca2919d8af6b8 100644
*** a/src/backend/commands/variable.c
--- b/src/backend/commands/variable.c
*** show_log_timezone(void)
*** 533,543
* read-only may be changed to read-write only when in a top-level transaction
* that has not yet taken an initial snapshot. Can't do it in a hot standby
* slave, either.
*/
bool
check_transaction_read_only(bool *newval, void **extra, GucSource source)
{
! if (*newval == false && XactReadOnly)
{
/* Can't go to r/w mode inside a r/o transaction */
if (IsSubTransaction())
--- 533,548
* read-only may be changed to read-write only when in a top-level transaction
* that has not yet taken an initial snapshot. Can't do it in a hot standby
* slave, either.
+ *
+ * If we are not in a transaction at all, just allow the change; it means
+ * nothing since XactReadOnly will be reset by the next StartTransaction().
+ * The IsTransactionState() test protects us against trying to check
+ * RecoveryInProgress() in contexts where shared memory is not accessible.
*/
bool
check_transaction_read_only(bool *newval, void **extra, GucSource source)
{
! if (*newval == false && XactReadOnly && IsTransactionState())
{
/* Can't go to r/w mode inside a r/o transaction */
if (IsSubTransaction())
*** check_transaction_read_only(bool *newval
*** 556,561
--- 561,567
/* Can't go to r/w mode while recovery is still active */
if (RecoveryInProgress())
{
+ GUC_check_errcode(ERRCODE_FEATURE_NOT_SUPPORTED);
GUC_check_errmsg("cannot set transaction read-write mode during recovery");
return false;
}
*** check_transaction_read_only(bool *newval
*** 569,574
--- 575,582
*
* We allow idempotent changes at any time, but otherwise this can only be
* changed in a toplevel transaction that has not yet taken a snapshot.
+ *
+ * As in check_transaction_read_only, allow it if not inside a transaction.
*/
bool
check_XactIsoLevel(char **newval, void **extra, GucSource source)
*** check_XactIsoLevel(char **newval, void *
*** 598,604
else
return false;
! if (newXactIsoLevel != XactIsoLevel)
{
if (FirstSnapshotSet)
{
--- 606,612
else
return false;
! if (newXactIsoLevel != XactIsoLevel && IsTransactionState())
{
if (FirstSnapshotSet)
{
*** check_XactIsoLevel(char **newval, void *
*** 616,621
--- 624,630
/* Can't go to serializable mode while recovery is still active */
if (newXactIsoLevel == XACT_SERIALIZABLE && RecoveryInProgress())
{
+ GUC_check_errcode(ERRCODE_FEATURE_NOT_SUPPORTED);
GUC_check_errmsg("cannot use serializable mode in a hot standby");
GUC_check_errhint("You can use REPEATABLE READ instead.");
return false;
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index b22faf9607d87f1a2bc7ce306e923dc12b8cfcc7..8b5a95ceaa0ff460d34231dadc2d3562fa7b0c63 100644
*** a/src/backend/storage/lmgr/predicate.c
--- b/src/backend/storage/lmgr/predicate.c
*** GetSerializableTra
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
"Kevin Grittner" writes: > How about we fix the serializable versus HS & Windows bugs in one > patch, and then look at the other as a separate patch? If that's OK, > I think this is ready, unless my message text can be improved. (And > I will have a shot at my first back-patching) I poked around this area a bit. I notice that check_transaction_read_only has got the same fundamental error: it thinks it can safely consult RecoveryInProgress(), which in general it cannot. The particular cases we have discussed so far cannot lead to a crash there, because in startup scenarios XactReadOnly wouldn't be on already. However I think that a background process not connected to shared memory could be crashed if somebody changed transaction_read_only from true to false in postgresql.conf. That's sufficiently far-fetched that maybe we shouldn't worry about it, but still it seems ugly. On reflection I think maybe the best solution is for check_transaction_read_only to test IsTransactionState(), and just allow the change always if outside a transaction. That would make its IsSubTransaction test a bit saner/safer as well. We could do the same thing in check_XactIsoLevel. We still need a test in GetSerializableTransactionSnapshot, or someplace else in the vicinity of that, to cover the default_transaction_isolation = serializable case; but if we leave the error check in place in check_XactIsoLevel, you'll get an immediate rather than delayed error from trying to crank the level up manually in hot standby, which seems more user-friendly. Will send an updated patch as soon as I'm done testing this idea. One other point: I notice that Kevin used ERRCODE_FEATURE_NOT_SUPPORTED in the error messages he added, which seems sane in isolation. However, the GUC-based code is (by default) throwing ERRCODE_INVALID_PARAMETER_VALUE when it rejects due to RecoveryInProgress. I'm not totally sure whether that was thought about or just fell out of not thinking. Which one do we want here? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
> "Kevin Grittner" wrote: > Heikki Linnakangas wrote: >> On 14.08.2012 14:25, Kevin Grittner wrote: Attached is version 3. >>> Oh, further testing this morning shows that while *queries* on >>> the HS seem OK, streaming replication is now broken. I probably >>> need to override transaction isolation on the recovery process. >>> I'll take a look at that. >> >> Hmm, seems to work for me. Do you get an unexpected error or what? > > No, I wasn't getting errors in the clients or the logs, but I > wasn't seeing data pop up on the replica when I expected. Perhaps I > messed up my streaming replication configuration somehow. Yeah, setup error. I accidentally dropped the primary_conninfo setting from my recovery.conf file. Now that I've put that back, it works just fine. >> I didn't, I meant to point out that you can set >> transaction_isolation just for the one transaction. But your >> suggested hint is OK as well - you suggest to set it for the whole >> session, which will also work around the problem. The "before the >> first query in the transaction" isn't necessary in that case >> though. >> Yet another option is to suggest the "BEGIN ISOLATION LEVEL >> REPEATABLE READ" syntax, instead of SET. > > I'm inclined toward hinting at a session override of the default. > If you're typing away in psql, that's a lot less work. :-) I tinkered with the messages (including correcting a reverse-logic bug in which was displayed under what circumstances) and tweaked a comment. I struggled with how to capitalize and quote. Let me know what you think. > Since the existing behavior is so bad, I'm inclined to think > this merits backpatching to 9.1. Thoughts on that? Yes, we have to somehow fix the crash and the assertion failure on 9.1. >>> >>> Should the check_transaction_read_only() stuff be back-patched to >>> 9.1, too? So far as we know, that's fragile, not broken, right? >>> Could the fix you envision there cause a behavioral change that >>> could break anything that users might have in place? >> >> Good question. I don't see how it could cause a behavioral change, >> but I've been wrong before. > > If we don't know of any actual existing bugs I'm inclined to not > back-patch that part to 9.1, although it makes sense for 9.2 since > we shouldn't be risking breakage of any production systems. I'm > really cautious about giving anybody any excuse not to apply a > minor update. How about we fix the serializable versus HS & Windows bugs in one patch, and then look at the other as a separate patch? If that's OK, I think this is ready, unless my message text can be improved. (And I will have a shot at my first back-patching) -Kevin hotstandby-serializable-3.patch Description: Binary data -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas wrote: > On 14.08.2012 14:25, Kevin Grittner wrote: >> Heikki Linnakangas wrote: >>> On 14.08.2012 08:23, Kevin Grittner wrote: >> Oh, further testing this morning shows that while *queries* on >> the HS seem OK, streaming replication is now broken. I probably >> need to override transaction isolation on the recovery process. >> I'll take a look at that. > > Hmm, seems to work for me. Do you get an unexpected error or what? No, I wasn't getting errors in the clients or the logs, but I wasn't seeing data pop up on the replica when I expected. Perhaps I messed up my streaming replication configuration somehow. Do I understand that you are now seeing correction of both bugs and no new misbehaviors in your tests? >>> Now that the error is thrown when the first snapshot is taken, >>> rather than at the SET command, I think the error message needs >>> some work: >>> >>> postgres=# select 123; >>> ERROR: cannot use serializable mode in a hot standby >>> HINT: You can use REPEATABLE READ instead. >>> >>> If the isolation level came from default_transaction_isolation, >>> set in postgresql.conf file, it might take the user a while to >>> figure that out. Perhaps something like this: >>> >>> ERROR: cannot use serializable mode in a hot standby >>> DETAIL: default_transaction_isolation was set to 'serializable' >>> in the config file. >>> HINT: You can use "SET transaction_isolation = 'repeatable >>> read'" before the first query in the transaction to override it. >> >> Did you mean?: >> >> HINT: You can use "SET default_transaction_isolation = >> 'repeatable read'" before the first query in the transaction to >> override it. > I didn't, I meant to point out that you can set > transaction_isolation just for the one transaction. But your > suggested hint is OK as well - you suggest to set it for the whole > session, which will also work around the problem. The "before the > first query in the transaction" isn't necessary in that case > though. Yeah, I figured that out before posting version 2 of the patch. I should have said something. > Yet another option is to suggest the "BEGIN ISOLATION LEVEL > REPEATABLE READ" syntax, instead of SET. I'm inclined toward hinting at a session override of the default. If you're typing away in psql, that's a lot less work. :-) That's what I included in version 2 of the patch, but only if the default was serializable. I did say to set it "before a transaction" because a quick test showed that setting the default in a transaction didn't keep that transaction from getting the error if you proceeded to run a SELECT statement. Since the existing behavior is so bad, I'm inclined to think this merits backpatching to 9.1. Thoughts on that? >>> >>> Yes, we have to somehow fix the crash and the assertion failure >>> on 9.1. >> >> Should the check_transaction_read_only() stuff be back-patched to >> 9.1, too? So far as we know, that's fragile, not broken, right? >> Could the fix you envision there cause a behavioral change that >> could break anything that users might have in place? > > Good question. I don't see how it could cause a behavioral change, > but I've been wrong before. If we don't know of any actual existing bugs I'm inclined to not back-patch that part to 9.1, although it makes sense for 9.2 since we shouldn't be risking breakage of any production systems. I'm really cautious about giving anybody any excuse not to apply a minor update. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
On 14.08.2012 14:25, Kevin Grittner wrote: Heikki Linnakangas wrote: On 14.08.2012 08:23, Kevin Grittner wrote: OK, attached is a first cut to confirm that the approach looks sane to everyone; I *think* it is along the lines that we reached consensus. After moving the check to the point where we get a serializable snapshot, it was still behaving badly. It took a bit, but forcing the snapshot acquisition in InitPostgres to use 'read committed' instead of the default isolation level got reasonable behavior in my initial tests. It sure looks a lot better to *me* than what was happening before. Oh, further testing this morning shows that while *queries* on the HS seem OK, streaming replication is now broken. I probably need to override transaction isolation on the recovery process. I'll take a look at that. Hmm, seems to work for me. Do you get an unexpected error or what? Now that the error is thrown when the first snapshot is taken, rather than at the SET command, I think the error message needs some work: postgres=# select 123; ERROR: cannot use serializable mode in a hot standby HINT: You can use REPEATABLE READ instead. If the isolation level came from default_transaction_isolation, set in postgresql.conf file, it might take the user a while to figure that out. Perhaps something like this: ERROR: cannot use serializable mode in a hot standby DETAIL: default_transaction_isolation was set to 'serializable' in the config file. HINT: You can use "SET transaction_isolation = 'repeatable read'" before the first query in the transaction to override it. Did you mean?: HINT: You can use "SET default_transaction_isolation = 'repeatable read'" before the first query in the transaction to override it. Otherwise, I agree and will do. I didn't, I meant to point out that you can set transaction_isolation just for the one transaction. But your suggested hint is OK as well - you suggest to set it for the whole session, which will also work around the problem. The "before the first query in the transaction" isn't necessary in that case though. Yet another option is to suggest the "BEGIN ISOLATION LEVEL REPEATABLE READ" syntax, instead of SET. Since the existing behavior is so bad, I'm inclined to think this merits backpatching to 9.1. Thoughts on that? Yes, we have to somehow fix the crash and the assertion failure on 9.1. Should the check_transaction_read_only() stuff be back-patched to 9.1, too? So far as we know, that's fragile, not broken, right? Could the fix you envision there cause a behavioral change that could break anything that users might have in place? Good question. I don't see how it could cause a behavioral change, but I've been wrong before. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas wrote: > we have to somehow fix the crash and the assertion failure on 9.1. Here's a revision with some changes based on your feedback. I have to go to my "day job" now, and I was unable to find the right place to fix the streaming replication problem. I fear I won't be able to get this sorted out before the wrap of back-branch releases this evening, so if you feel it is urgent enough to need to get into that, feel free to finish it; otherwise I'll keep at it tonight. -Kevin hotstandby-serializable-2.patch Description: Binary data -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas wrote: > On 14.08.2012 08:23, Kevin Grittner wrote: >> OK, attached is a first cut to confirm that the approach looks >> sane to everyone; I *think* it is along the lines that we reached >> consensus. After moving the check to the point where we get a >> serializable snapshot, it was still behaving badly. It took a bit, >> but forcing the snapshot acquisition in InitPostgres to use 'read >> committed' instead of the default isolation level got reasonable >> behavior in my initial tests. It sure looks a lot better to *me* >> than what was happening before. Oh, further testing this morning shows that while *queries* on the HS seem OK, streaming replication is now broken. I probably need to override transaction isolation on the recovery process. I'll take a look at that. > A comment in InitPostgres would be nice, explaining why we want a > read committed snapshot there. OK. > This fixes both the assertion failure and the Windows crash, which > is good. I wasn't sure whether it would help with the Windows crash or not. I'm not set up to build under Windows, so I'm glad you gave that a check. > Now that the error is thrown when the first snapshot is taken, > rather than at the SET command, I think the error message needs > some work: > > postgres=# select 123; > ERROR: cannot use serializable mode in a hot standby > HINT: You can use REPEATABLE READ instead. > > If the isolation level came from default_transaction_isolation, set > in postgresql.conf file, it might take the user a while to figure > that out. Perhaps something like this: > > ERROR: cannot use serializable mode in a hot standby > DETAIL: default_transaction_isolation was set to 'serializable' in > the config file. > HINT: You can use "SET transaction_isolation = 'repeatable read'" > before the first query in the transaction to override it. Did you mean?: HINT: You can use "SET default_transaction_isolation = 'repeatable read'" before the first query in the transaction to override it. Otherwise, I agree and will do. > This still leaves the RecoveryInProgress() call in > check_transaction_read_only(), which isn't a problem at the moment, > but seems fragile. I think we should still add the > IsTransactionState() check in there, so that it works without > shared memory access. If we're not in a transaction yet > (TRANS_DEFAULT), setting transaction_read_only has no effect, as > it's overwritten at the beginning of a transaction. If we're in one > of the transitory states, TRANS_START or > TRANS_COMMIT/ABORT/PREPARE, I'm not sure what should happen, but it > should not be possible for user code to run and change > transaction_read_only in those states. I'll take a look. >> Since the existing behavior is so bad, I'm inclined to think this >> merits backpatching to 9.1. Thoughts on that? > > Yes, we have to somehow fix the crash and the assertion failure on > 9.1. Should the check_transaction_read_only() stuff be back-patched to 9.1, too? So far as we know, that's fragile, not broken, right? Could the fix you envision there cause a behavioral change that could break anything that users might have in place? -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
On 14.08.2012 08:23, Kevin Grittner wrote: OK, attached is a first cut to confirm that the approach looks sane to everyone; I *think* it is along the lines that we reached consensus. After moving the check to the point where we get a serializable snapshot, it was still behaving badly. It took a bit, but forcing the snapshot acquisition in InitPostgres to use 'read committed' instead of the default isolation level got reasonable behavior in my initial tests. It sure looks a lot better to *me* than what was happening before. A comment in InitPostgres would be nice, explaining why we want a read committed snapshot there. Besides confirming that this is the solution people want, this has not been tested well enough yet to be ready for commit. It's getting late, though, and I'm fading. If the overall approach looks good I'll beat up on it some more tomorrow. Thanks! This fixes both the assertion failure and the Windows crash, which is good. Now that the error is thrown when the first snapshot is taken, rather than at the SET command, I think the error message needs some work: postgres=# select 123; ERROR: cannot use serializable mode in a hot standby HINT: You can use REPEATABLE READ instead. If the isolation level came from default_transaction_isolation, set in postgresql.conf file, it might take the user a while to figure that out. Perhaps something like this: ERROR: cannot use serializable mode in a hot standby DETAIL: default_transaction_isolation was set to 'serializable' in the config file. HINT: You can use "SET transaction_isolation = 'repeatable read'" before the first query in the transaction to override it. This still leaves the RecoveryInProgress() call in check_transaction_read_only(), which isn't a problem at the moment, but seems fragile. I think we should still add the IsTransactionState() check in there, so that it works without shared memory access. If we're not in a transaction yet (TRANS_DEFAULT), setting transaction_read_only has no effect, as it's overwritten at the beginning of a transaction. If we're in one of the transitory states, TRANS_START or TRANS_COMMIT/ABORT/PREPARE, I'm not sure what should happen, but it should not be possible for user code to run and change transaction_read_only in those states. Since the existing behavior is so bad, I'm inclined to think this merits backpatching to 9.1. Thoughts on that? Yes, we have to somehow fix the crash and the assertion failure on 9.1. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
"Kevin Grittner" wrote: > OK, attached [sigh] This time for sure! -Kevin hotstandby-serializable.patch Description: Binary data -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas wrote: > While playing around, I bumped into another related bug, and after > googling around I found out that it was already reported by Robert > Haas earlier, but still not fixed: > Kevin, the last message on that thread says you'll write a patch > for that. Ping? OK, attached is a first cut to confirm that the approach looks sane to everyone; I *think* it is along the lines that we reached consensus. After moving the check to the point where we get a serializable snapshot, it was still behaving badly. It took a bit, but forcing the snapshot acquisition in InitPostgres to use 'read committed' instead of the default isolation level got reasonable behavior in my initial tests. It sure looks a lot better to *me* than what was happening before. Besides confirming that this is the solution people want, this has not been tested well enough yet to be ready for commit. It's getting late, though, and I'm fading. If the overall approach looks good I'll beat up on it some more tomorrow. Since the existing behavior is so bad, I'm inclined to think this merits backpatching to 9.1. Thoughts on that? -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas wrote: > While playing around, I bumped into another related bug, and > after googling around I found out that it was already reported by > Robert Haas earlier, but still not fixed: > http://archives.postgresql.org/message-id/CA%2BTgmoa0UM2W1YkjjneEgJctzxopC3G53ocYPaCyoEOWT3aKiA%40mail.gmail.com > Kevin, the last message on that thread ( > http://archives.postgresql.org/pgsql-hackers/2012-04/msg01394.php > ) says you'll write a patch for that. Ping? Or would you like me > to try that? Let me try to redeem myself by taking a shot at it tonight. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
From: pgsql-hackers-ow...@postgresql.org [mailto:pgsql-hackers-ow...@postgresql.org] On Behalf Of Amit Kapila Sent: Monday, August 13, 2012 12:47 PM From: pgsql-hackers-ow...@postgresql.org [mailto:pgsql-hackers-ow...@postgresql.org] On Behalf Of Heikki Linnakangas Sent: Monday, August 13, 2012 12:14 PM On 12.08.2012 17:39, Tom Lane wrote: > Heikki Linnakangas writes: >>> Hm, how did the same code fail to crash in the postmaster itself, when >>> the postmaster read the setting from postgresql.conf? >>It's not the check function for default_transaction_isolation that >>crashes, but the one for transaction_isolation. >> I 'm not exactly sure how transaction_isolation gets set to a non-default >> value, though. The default for transaction_isolation is 'default', so >> it's understandable that the underlying XactIsoLevel variable gets set >> to XACT_SERIALIZABLE, but AFAICS the code to read/write the GUCs from/to >> file only cares about the string value of the guc, not the integer value >> of the underlying global variable. > Here What I am able to trace is that function read_nondefault_variables(), > reads all variables > from config_exec_params which contains both default_transaction_isolation > and transaction_isolation. > 1. it first reads default_transaction_isolation and sets value of > DefaultXactIsoLevel to 'serializable'. > 2. As for parameter default_transaction_isolation, there is no check > function it passes. > 3. After that when variable transaction_isolation is processed, function > check_XactIsoLevel() sets > XactIsoLevel to XACT_SERIALIZABLE which causes crash. > Actually function read_nondefault_variables(), should only process non > default values (default_transaction_isolation) > not transaction_isolation, but currently it processes both? transaction_isolation is getting written to config_exec_params file as function write_one_nondefault_variable() checks if conf source is not PGC_S_DEFAULT, then it writes to file. For transaction_isolation, the conf source is set to PGC_S_OVERRIDE in function InitializeGUCOptions() so this also gets written to config_exec_params file. Should the parameter transaction_isolation be written to config_exec_params? With Regards, Amit Kapila. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
From: pgsql-hackers-ow...@postgresql.org [mailto:pgsql-hackers-ow...@postgresql.org] On Behalf Of Heikki Linnakangas Sent: Monday, August 13, 2012 12:14 PM On 12.08.2012 17:39, Tom Lane wrote: > Heikki Linnakangas writes: >>> The problem is that when a postmaster subprocess is launched, it calls >>> read_nondefault_variables() very early, before shmem initialization, to >>> read the non-default config options from the file that postmaster wrote. >>> When check_XactIsoLevel() calls RecoveryInProgress(), it crashes, >>> because XLogCtl is NULL. > >> Hm, how did the same code fail to crash in the postmaster itself, when >> the postmaster read the setting from postgresql.conf? >It's not the check function for default_transaction_isolation that >crashes, but the one for transaction_isolation. > I 'm not exactly sure how transaction_isolation gets set to a non-default > value, though. The default for transaction_isolation is 'default', so > it's understandable that the underlying XactIsoLevel variable gets set > to XACT_SERIALIZABLE, but AFAICS the code to read/write the GUCs from/to > file only cares about the string value of the guc, not the integer value > of the underlying global variable. Here What I am able to trace is that function read_nondefault_variables(), reads all variables from config_exec_params which contains both default_transaction_isolation and transaction_isolation. 1. it first reads default_transaction_isolation and sets value of DefaultXactIsoLevel to 'serializable'. 2. As for parameter default_transaction_isolation, there is no check function it passes. 3. After that when variable transaction_isolation is processed, function check_XactIsoLevel() sets XactIsoLevel to XACT_SERIALIZABLE which causes crash. Actually function read_nondefault_variables(), should only process non default values (default_transaction_isolation) not transaction_isolation, but currently it processes both? With Regards, Amit Kapila. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas writes: > On 12.08.2012 17:39, Tom Lane wrote: >> A larger point is that I think it's broken for any GUC assignment >> function to be calling something as transient as RecoveryInProgress to >> start with. > Hmm, it seems like the logical place to complain if you do a manual "SET > transaction_isolation='serializable'". But I think we should only do the > check if we're not in a transaction. You mean "if we *are* in a transaction"? Possibly that would work. The concerns I've got about running this type of test in a GUC hook are (1) what if you're not in a transaction or (2) what if you aren't in a process that has access to shared memory; the early-startup-in- EXEC_BACKEND case loses on both counts. But I think we can test our local in-transaction state without touching shared memory, and then go from there. > While playing around, I bumped into another related bug, and after > googling around I found out that it was already reported by Robert Haas > earlier, but still not fixed: > http://archives.postgresql.org/message-id/CA%2BTgmoa0UM2W1YkjjneEgJctzxopC3G53ocYPaCyoEOWT3aKiA%40mail.gmail.com That sounds like a different bug, although perhaps with the same theme of overreliance on what a GUC hook can do. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
On 12.08.2012 17:39, Tom Lane wrote: Heikki Linnakangas writes: The problem is that when a postmaster subprocess is launched, it calls read_nondefault_variables() very early, before shmem initialization, to read the non-default config options from the file that postmaster wrote. When check_XactIsoLevel() calls RecoveryInProgress(), it crashes, because XLogCtl is NULL. Hm, how did the same code fail to crash in the postmaster itself, when the postmaster read the setting from postgresql.conf? It's not the check function for default_transaction_isolation that crashes, but the one for transaction_isolation. I'm not exactly sure how transaction_isolation gets set to a non-default value, though. The default for transaction_isolation is 'default', so it's understandable that the underlying XactIsoLevel variable gets set to XACT_SERIALIZABLE, but AFAICS the code to read/write the GUCs from/to file only cares about the string value of the guc, not the integer value of the underlying global variable. A larger point is that I think it's broken for any GUC assignment function to be calling something as transient as RecoveryInProgress to start with. We probably ought to re-think the logic, not just band-aid this by having it skip the check when shmem isn't initialized yet. I'm thinking that the check has to occur somewhere outside GUC. Hmm, it seems like the logical place to complain if you do a manual "SET transaction_isolation='serializable'". But I think we should only do the check if we're not in a transaction. Setting the guc won't have any effect outside a transaction anyway, because StartTransaction will overwrite it from default_transaction_isolation as soon as you begin a transaction. While playing around, I bumped into another related bug, and after googling around I found out that it was already reported by Robert Haas earlier, but still not fixed: http://archives.postgresql.org/message-id/CA%2BTgmoa0UM2W1YkjjneEgJctzxopC3G53ocYPaCyoEOWT3aKiA%40mail.gmail.com. Kevin, the last message on that thread (http://archives.postgresql.org/pgsql-hackers/2012-04/msg01394.php) says you'll write a patch for that. Ping? Or would you like me to try that? -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] default_isolation_level='serializable' crashes on Windows
Heikki Linnakangas writes: > The problem is that when a postmaster subprocess is launched, it calls > read_nondefault_variables() very early, before shmem initialization, to > read the non-default config options from the file that postmaster wrote. > When check_XactIsoLevel() calls RecoveryInProgress(), it crashes, > because XLogCtl is NULL. Hm, how did the same code fail to crash in the postmaster itself, when the postmaster read the setting from postgresql.conf? A larger point is that I think it's broken for any GUC assignment function to be calling something as transient as RecoveryInProgress to start with. We probably ought to re-think the logic, not just band-aid this by having it skip the check when shmem isn't initialized yet. I'm thinking that the check has to occur somewhere outside GUC. regards, tom lane - Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
