Horton

Re: new heapcheck contrib module

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Mark Dilger <mark.dilger@enterprisedb.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Peter Geoghegan <pg@bowt.ie>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2020-07-30T21:00:11Z
Lists: pgsql-hackers 
On Thu, Jul 30, 2020 at 4:18 PM Mark Dilger
<mark.dilger@enterprisedb.com> wrote:
> > Maybe I'm just being dense here -- exactly what problem are you worried about?
>
> Per tuple, tuple_is_visible() potentially checks whether the xmin or xmax committed via TransactionIdDidCommit.  I am worried about concurrent truncation of clog entries causing I/O errors on SLRU lookup when performing that check.  The three strategies I had for dealing with that were taking the XactTruncationLock (formerly known as CLogTruncationLock, for those reading this thread from the beginning), locking out vacuum, and the idea upthread from Andres about setting PROC_IN_VACUUM and such.  Maybe I'm being dense and don't need to worry about this.  But I haven't convinced myself of that, yet.

I don't get it. If you've already checked that the XIDs are >=
relfrozenxid and <= ReadNewFullTransactionId(), then this shouldn't be
a problem. It could be, if CLOG is hosed, which is possible, because
if the table is corrupted, why shouldn't CLOG also be corrupted? But
I'm not sure that's what your concern is here.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Add pg_amcheck, a CLI for contrib/amcheck.

  2. Refactor and generalize the ParallelSlot machinery.

  3. Generalize parallel slot result handling.

  4. Move some code from src/bin/scripts to src/fe_utils to permit reuse.

  5. Factor pattern-construction logic out of processSQLNamePattern.

  6. Doc: clean up verify_heapam() documentation.

  7. Fix more portability issues in new amcheck code.

  8. Fix portability issues in new amcheck test.

  9. Try to avoid a compiler warning about using fxid uninitialized.

  10. Extend amcheck to check heap pages.

  11. Adjust walsender usage of xlogreader, simplify APIs

  12. Improve checking of child pages in contrib/amcheck.

  13. Sanitize line pointers within contrib/amcheck.

  14. Fix possible sorting error when aborting use of abbreviated keys.