Date: Mon, 27 Nov 2017 18:52:18 +0300
From: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org, Ildar Musin <i.musin@postgrespro.ru>
Subject: Re: [HACKERS] Custom compression methods
Message-ID: <20171127185218.5cddad41@wp.localdomain>
In-Reply-To: <b969fa5a-bc2a-c220-c992-e6e0de34df14@2ndquadrant.com>
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On Sat, 25 Nov 2017 06:40:00 +0100
Tomas Vondra <tomas.vondra@2ndquadrant.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