Re: PANIC in GIN code

On 06/29/2015 01:12 AM, Jeff Janes wrote:
> Now I'm getting a different error, with or without checksums.
>
> ERROR:  invalid page in block 0 of relation base/16384/16420
> CONTEXT:  automatic vacuum of table "jjanes.public.foo"
>
> 16420 is the gin index.  I can't even get the page with pageinspect:
>
> jjanes=# SELECT * FROM get_raw_page('foo_text_array_idx', 0);
> ERROR:  invalid page in block 0 of relation base/16384/16420
>
> This is the last few gin entries from pg_xlogdump
>
>
> rmgr: Gin         len (rec/tot):      0/  3893, tx:          0, lsn:
> 0/77270E90, prev 0/77270E68, desc: VACUUM_PAGE , blkref #0: rel
> 1663/16384/16420 blk 27 FPW
> rmgr: Gin         len (rec/tot):      0/  3013, tx:          0, lsn:
> 0/77272080, prev 0/77272058, desc: VACUUM_PAGE , blkref #0: rel
> 1663/16384/16420 blk 6904 FPW
> rmgr: Gin         len (rec/tot):      0/  3093, tx:          0, lsn:
> 0/77272E08, prev 0/77272DE0, desc: VACUUM_PAGE , blkref #0: rel
> 1663/16384/16420 blk 1257 FPW
> rmgr: Gin         len (rec/tot):      8/  4662, tx:  318119897, lsn:
> 0/77A2CF10, prev 0/77A2CEC8, desc: INSERT_LISTPAGE , blkref #0: rel
> 1663/16384/16420 blk 22184
> rmgr: Gin         len (rec/tot):     88/   134, tx:  318119897, lsn:
> 0/77A2E188, prev 0/77A2E160, desc: UPDATE_META_PAGE , blkref #0: rel
> 1663/16384/16420 blk 0
>
>
> And the metapage is mostly zeros:
>
> head -c 8192 /tmp/data2_invalid_page/base/16384/16420 | od
> 0000000 000000 000000 161020 073642 000000 000000 000000 000000
> 0000020 000000 000000 000000 000000 053250 000000 053250 000000
> 0000040 006140 000000 000001 000000 000001 000000 000000 000000
> 0000060 031215 000000 000452 000000 000000 000000 000000 000000
> 0000100 025370 000000 000000 000000 000002 000000 000000 000000
> 0000120 000000 000000 000000 000000 000000 000000 000000 000000
> *
> 0020000

Hmm. Looking at ginRedoUpdateMetapage, I think I see the problem: it 
doesn't initialize the page. It copies the metapage data, but it doesn't 
touch the page headers. The only way I can see that that would cause 
trouble is if the index somehow got truncated away or removed in the 
standby. That could happen in crash recovery, if you drop the index and 
the crash, but that should be harmless, because crash recovery doesn't 
try to read the metapage, only update it (by overwriting it), and by the 
time crash recovery has completed, the index drop is replayed too.

But AFAICS that bug is present in earlier versions too. Can you 
reproduce this easily? How?

- Heikki