Try reading them "row by row" until it breaks. That is, SELECT * FROM ... LIMIT 1, then LIMIT 2 etc. For more efficiency use a binary search starting at what seems like a reasonable place looking at the size of the table vs the first failed block to make it faster, but the principle is the same. Once it fails, you've found a corrupt block...
//Magnus On Tue, Sep 15, 2020 at 12:46 PM Vasu Madhineni <vasumdba1...@gmail.com> wrote: > Is it possible to identify which rows are corrupted in particular tables. > > On Tue, Sep 15, 2020 at 5:36 PM Magnus Hagander <mag...@hagander.net> > wrote: > >> >> >> On Tue, Sep 15, 2020 at 11:15 AM Vasu Madhineni <vasumdba1...@gmail.com> >> wrote: >> >>> Hi All, >>> >>> In one of my postgres databases multiple tables got corrupted and >>> followed the below steps but still the same error. >>> >>> 1.SET zero_damaged_pages = on >>> 2. VACUUM ANALYZE, VACUUM FULL >>> but still same error. >>> >> >> >> That is a very destructive first attempt. I hope you took a full >> disk-level backup of the database before you did that, as it can ruin your >> chances for forensics and data recovery for other issues. >> >> >> moh_fa=# VACUUM FULL; >>> ERROR: could not read block 9350 in file "base/1156523/1270812": >>> Input/output error >>> >>> Tried to take backup of tables with pg_dump but same error. files exist >>> physically in base location. >>> >>> How to proceed on this, no backup to restore. >>> >>> >> This is clearly some sort of disk error, and with no backups to restore >> you will definitely be losing data. >> >> I'd start by figuring out which tables have no corruption and do work, >> and back those up (with pg_dump for example) as soon as possible to a >> different machine -- since it's not exactly unlikely that further disk >> errors will appear. >> >> Once you've done that, identify the tables, and then try to do partial >> recovery. For example, if you look at the file 1270812, how big it is? >> PostgreSQL is failing to read block 9350 which is 76595200 bytes into the >> file. If this is at the very end of the file, you can for example try to >> get the data out until that point with LIMIT. If it's in the middle of the >> file, it gets more ticky, but similar approaches can be done. >> >> Also, unless you are running with data checksums enabled, I wouldn't >> fully trust the data in the tables that you *can* read either. Since you >> clearly have disk issues, they may have caused corruption elsewhere as >> well, so whatever verification you can do against other tables, you should >> do as well. >> >> >> You'll of course also want to check any kernel logs or storage system >> logs to see if they can give you a hint as to what happened, but they are >> unlikely to actually give you something that will help you fix the problem. >> >>
