On Tue, 21 Nov 2017 18:47:49 +0100 Tomas Vondra <tomas.von...@2ndquadrant.com> wrote:
> > I propose to use either > > CompressionMethodOptions (and CompressionMethodRoutine) > > or > > CompressionOptions (and CompressionRoutine) Sounds good, thanks. > > OK. But then I don't understand why tsvector.c does things like > > VARSIZE(data) - VARHDRSZ_CUSTOM_COMPRESSED - arrsize > VARRAWSIZE_4B_C(data) - arrsize > > instead of > > VARSIZE_ANY_EXHDR(data) - arrsize > VARSIZE_ANY(data) - arrsize > > Seems somewhat confusing. > VARRAWSIZE_4B_C returns original size of data, before compression (from va_rawsize in current postgres, and from va_info in my patch), not size of the already compressed data, so you can't use VARSIZE_ANY here. VARSIZE_ANY_EXHDR in current postgres returns VARSIZE-VARHDRSZ, despite the varlena is compressed or not, so I just kept this behavior for custom compressed varlenas too. If you look into tuptoaster.c you will also see lines like 'VARSIZE(attr) - TOAST_COMPRESS_HDRSZ'. So I think if VARSIZE_ANY_EXHDR will subtract different header sizes then it should subtract them for usual compressed varlenas too. > > > > Hmmm, it still doesn't work for me. See this: > > test=# create extension pg_lz4 ; > CREATE EXTENSION > test=# create table t_lz4 (v text compressed lz4); > CREATE TABLE > test=# create table t_pglz (v text); > CREATE TABLE > test=# insert into t_lz4 select repeat(md5(1::text),300); > INSERT 0 1 > test=# insert into t_pglz select * from t_lz4; > INSERT 0 1 > test=# drop extension pg_lz4 cascade; > NOTICE: drop cascades to 2 other objects > DETAIL: drop cascades to compression options for lz4 > drop cascades to table t_lz4 column v > DROP EXTENSION > test=# \c test > You are now connected to database "test" as user "user". > test=# insert into t_lz4 select repeat(md5(1::text),300);^C > test=# select * from t_pglz ; > ERROR: cache lookup failed for compression options 16419 > > That suggests no recompression happened. I will check that. Is your extension published somewhere?