Re: [HACKERS] Hanging backends and possible index corruption
--On 25. Januar 2013 20:37:32 -0500 Tom Lane t...@sss.pgh.pa.us wrote: Don't know how careful pgbtreecheck is. The pg_filedump output isn't very helpful because you filtered away the flags, so we can't tell if any of these pages are deleted. (If they are, the duplicate-looking links might not be errors, since we intentionally don't reset a deleted page's left/right links when deleting it.) Ah, wasn't aware of this. Could we see the whole special-space dump for each of the pages you're worried about? Attached One thought that occurs to me is that POWER is a weak-memory-ordering architecture, so that it's a tenable idea that this has something to do with changing page links while not holding sufficient lock on the page. I don't see btree doing that anywhere, but ... BTW, how long has this installation been around, and when did you start seeing funny behavior? Can you say with reasonable confidence that the bug was *not* present in any older PG versions? This machine started in production around august last year with (afair) 9.1.5. There also were performance and stress tests on this machine before it went into production, with no noticable problems. However, what i missed before is that there were some trouble with the storage multipaths. Seems early january the machine lost some of it's paths to the SAN, but they were recovered a few seconds later...so i cannot exclude this as the cause anymore, though the paths are redundant. What strikes me is that the index was recreated in the meantime after this issue... We will watch this machine the next couple of weeks more closely, if the issue comes back again. -- Thanks Bernd dump.txt.bz2 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
[HACKERS] Hanging backends and possible index corruption
We are currently analyzing an issue at one of our customers PostgreSQL database. The current version is 9.1.6 (update to 9.1.7 is scheduled for next monday, no downtime possible before). It runs on POWER7 (pSeries 740) on an RHEL6.3 64-bit LPAR. The packages are built from PGDG SVN sources, no special tweaks added. We saw no hardware related errors on this machine, nor any crashes. What currently happens on this machine are hanging statements (SELECTs and INSERTs occasionally) with 100% CPU. After some investigation it turned out that the corresponding backends are seeking within an index file over and over again in a loop. Looking into the hanging queries i've recognized certain keys which seems to have the problem, other keys used in the WHERE condition run smoothly. Turning off index and bitmap index scans caused the suspicious keys to return results, too. So i've saved the index file (normal BTree index with a single bigint column), did a REINDEX and the problem was gone. Looking at the index file with pg_filedump and pgbtreecheck from Alvaro gave me the following output: pgbtreecheck gives warnings about pages' parents and then loops visiting the same pages over and over again: NOTICE: fast root: block 290 at level 2 NOTICE: setting page parents WARNING: block 12709 already had a parent (8840); new parent is 12177 WARNING: block 12710 already had a parent (12439); new parent is 10835 NOTICE: done setting parents NOTICE: Checking forward scan of level 0, starting at block 1 -- loop starts WARNING: right sibling 12710 does not point left to me (11680); points to 10924 instead Looking into the relevant pages and their prev and next pointers give me the following: pg_filedump -i -R 11680 ~/tmp/100252789 | grep Blocks Blocks: Previous (12651) Next (12710) Level (0) CycleId (0) pg_filedump -i -R 10924 ~/tmp/100252789 | grep Blocks Blocks: Previous (10923) Next (12710) Level (0) CycleId (0) pg_filedump -i -R 12710 ~/tmp/100252789 | grep Blocks Blocks: Previous (10924) Next (10925) Level (0) CycleId (0) pg_filedump -i -R 10925 ~/tmp/100252789 | grep Blocks Blocks: Previous (12710) Next (10926) Level (0) CycleId (0) pg_filedump -i -R 12709 ~/tmp/100252789 | grep Blocks Blocks: Previous (8849) Next (8850) Level (0) CycleId (0) pg_filedump -i -R 8840 ~/tmp/100252789 | grep Blocks Blocks: Previous (8555) Next (9125) Level (1) CycleId (0) pg_filedump -i -R 12439 ~/tmp/100252789 | grep Blocks Blocks: Previous (11405) Next (11690) Level (1) CycleId (0) $ pg_filedump -i -R 12177 ~/tmp/100252789 | grep Blocks Blocks: Previous (11690) Next (0) Level (1) CycleId (0) $ pg_filedump -i -R 10835 ~/tmp/100252789 | grep Blocks Blocks: Previous (10550) Next (11120) Level (1) CycleId (0) This symptom happened three times in the last couple of weeks now. Looking at the numbers doesn't give me the impression that some flaky hardware could be involved. What else can we do to track down this problem, any suggestions? -- Thanks Bernd -- 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] Hanging backends and possible index corruption
On 2013-01-25 16:24:52 +0100, Bernd Helmle wrote: We are currently analyzing an issue at one of our customers PostgreSQL database. The current version is 9.1.6 (update to 9.1.7 is scheduled for next monday, no downtime possible before). It runs on POWER7 (pSeries 740) on an RHEL6.3 64-bit LPAR. The packages are built from PGDG SVN sources, no special tweaks added. We saw no hardware related errors on this machine, nor any crashes. What currently happens on this machine are hanging statements (SELECTs and INSERTs occasionally) with 100% CPU. After some investigation it turned out that the corresponding backends are seeking within an index file over and over again in a loop. Looking into the hanging queries i've recognized certain keys which seems to have the problem, other keys used in the WHERE condition run smoothly. Turning off index and bitmap index scans caused the suspicious keys to return results, too. So i've saved the index file (normal BTree index with a single bigint column), did a REINDEX and the problem was gone. Looking at the index file with pg_filedump and pgbtreecheck from Alvaro gave me the following output: pgbtreecheck gives warnings about pages' parents and then loops visiting the same pages over and over again: NOTICE: fast root: block 290 at level 2 NOTICE: setting page parents WARNING: block 12709 already had a parent (8840); new parent is 12177 WARNING: block 12710 already had a parent (12439); new parent is 10835 NOTICE: done setting parents NOTICE: Checking forward scan of level 0, starting at block 1 -- loop starts WARNING: right sibling 12710 does not point left to me (11680); points to 10924 instead Looking into the relevant pages and their prev and next pointers give me the following: pg_filedump -i -R 11680 ~/tmp/100252789 | grep Blocks Blocks: Previous (12651) Next (12710) Level (0) CycleId (0) pg_filedump -i -R 10924 ~/tmp/100252789 | grep Blocks Blocks: Previous (10923) Next (12710) Level (0) CycleId (0) pg_filedump -i -R 12710 ~/tmp/100252789 | grep Blocks Blocks: Previous (10924) Next (10925) Level (0) CycleId (0) pg_filedump -i -R 10925 ~/tmp/100252789 | grep Blocks Blocks: Previous (12710) Next (10926) Level (0) CycleId (0) pg_filedump -i -R 12709 ~/tmp/100252789 | grep Blocks Blocks: Previous (8849) Next (8850) Level (0) CycleId (0) pg_filedump -i -R 8840 ~/tmp/100252789 | grep Blocks Blocks: Previous (8555) Next (9125) Level (1) CycleId (0) pg_filedump -i -R 12439 ~/tmp/100252789 | grep Blocks Blocks: Previous (11405) Next (11690) Level (1) CycleId (0) $ pg_filedump -i -R 12177 ~/tmp/100252789 | grep Blocks Blocks: Previous (11690) Next (0) Level (1) CycleId (0) $ pg_filedump -i -R 10835 ~/tmp/100252789 | grep Blocks Blocks: Previous (10550) Next (11120) Level (1) CycleId (0) This symptom happened three times in the last couple of weeks now. Looking at the numbers doesn't give me the impression that some flaky hardware could be involved. What else can we do to track down this problem, any suggestions? Did you reindex after upgrading to 9.1.6? Did you ever have any crashes or failovers before upgrading to 9.1.6? I have seen pretty similar symptoms caused by Fix persistence marking of shared buffers during WAL replay in 9.1.6. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training Services -- 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] Hanging backends and possible index corruption
--On 25. Januar 2013 16:28:16 +0100 Andres Freund and...@2ndquadrant.com wrote: Did you reindex after upgrading to 9.1.6? Did you ever have any crashes or failovers before upgrading to 9.1.6? I have seen pretty similar symptoms caused by Fix persistence marking of shared buffers during WAL replay in 9.1.6. Hmm it happened only on a single heavily used table for now and this table was REINDEXed twice after updating to 9.1.6 (every time the issue occured). -- Thanks Bernd -- 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] Hanging backends and possible index corruption
Bernd Helmle maili...@oopsware.de writes: So i've saved the index file (normal BTree index with a single bigint column), did a REINDEX and the problem was gone. Looking at the index file with pg_filedump and pgbtreecheck from Alvaro gave me the following output: ... Don't know how careful pgbtreecheck is. The pg_filedump output isn't very helpful because you filtered away the flags, so we can't tell if any of these pages are deleted. (If they are, the duplicate-looking links might not be errors, since we intentionally don't reset a deleted page's left/right links when deleting it.) Could we see the whole special-space dump for each of the pages you're worried about? One thought that occurs to me is that POWER is a weak-memory-ordering architecture, so that it's a tenable idea that this has something to do with changing page links while not holding sufficient lock on the page. I don't see btree doing that anywhere, but ... BTW, how long has this installation been around, and when did you start seeing funny behavior? Can you say with reasonable confidence that the bug was *not* present in any older PG versions? 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
