Re: [HACKERS] Custom compression methods

On Sat, 25 Nov 2017 06:40:00 +0100
Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:

> Hi,
>
> I ran into another issue - after inserting some data into a table
> with a tsvector column (without any compression defined), I can no
> longer read the data.
>
> This is what I get in the console:
>
> db=# select max(md5(body_tsvector::text)) from messages;
> ERROR: cache lookup failed for compression options 6432
>
> and the stack trace looks like this:
>
> Breakpoint 1, get_cached_compression_options (cmoptoid=6432) at
> tuptoaster.c:2563
> 2563 elog(ERROR, "cache lookup failed for
> compression options %u", cmoptoid);
> (gdb) bt
> #0 get_cached_compression_options (cmoptoid=6432) at
> tuptoaster.c:2563 #1 0x00000000004bf3da in toast_decompress_datum
> (attr=0x2b44148) at tuptoaster.c:2390
> #2 0x00000000004c0c1e in heap_tuple_untoast_attr (attr=0x2b44148) at
> tuptoaster.c:225
> #3 0x000000000083f976 in pg_detoast_datum (datum=<optimized out>) at
> fmgr.c:1829
> #4 0x00000000008072de in tsvectorout (fcinfo=0x2b41e00) at
> tsvector.c:315 #5 0x00000000005fae00 in ExecInterpExpr
> (state=0x2b414b8, econtext=0x2b25ab0, isnull=<optimized out>) at
> execExprInterp.c:1131 #6 0x000000000060bdf4 in
> ExecEvalExprSwitchContext (isNull=0x7fffffe9bd37 "",
> econtext=0x2b25ab0, state=0x2b414b8)
> at ../../../src/include/executor/executor.h:299
>
> It seems the VARATT_IS_CUSTOM_COMPRESSED incorrectly identifies the
> value as custom-compressed for some reason.
>
> Not sure why, but the tsvector column is populated by a trigger that
> simply does
>
> NEW.body_tsvector
> := to_tsvector('english', strip_replies(NEW.body_plain));
>
> If needed, the complete tool is here:
>
> https://bitbucket.org/tvondra/archie
>

Hi. This looks like a serious bug, but I couldn't reproduce
it yet. Did you upgrade some old database or this bug happened after
insertion of all data to new database? I tried using your 'archie'
tool to download mailing lists and insert them to database, but couldn't
catch any errors.

--
---
Ildus Kurbangaliev
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company