Horton

Re: [HACKERS] Custom compression methods

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>
Cc: pgsql-hackers@postgresql.org, Ildar Musin <i.musin@postgrespro.ru>
Date: 2017-11-25T05:40:00Z
Lists: pgsql-hackers 
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


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. docs: Update TOAST storage docs for configurable compression.

  2. Further tweaking of pg_dump's handling of default_toast_compression.

  3. Fix interaction of TOAST compression with expression indexes.

  4. Tidy up more loose ends related to configurable TOAST compression.

  5. Short-circuit slice requests that are for more than the object's size.

  6. Mostly-cosmetic adjustments of TOAST-related macros.

  7. Remove useless configure probe for <lz4/lz4.h>.

  8. Error on invalid TOAST compression in CREATE or ALTER TABLE.

  9. docs: Fix omissions related to configurable TOAST compression.

  10. More code cleanup for configurable TOAST compression.

  11. Bring configure support for LZ4 up to snuff.

  12. Make compression.sql regression test independent of default.

  13. Use valid compression method in brin_form_tuple

  14. Fix up pg_dump's handling of per-attribute compression options.

  15. Allow configurable LZ4 TOAST compression.

  16. Fix inconsistencies in the code

  17. Mostly-cosmetic improvements in memory chunk header alignment coding.

  18. Allow numeric to use a more compact, 2-byte header in many cases.