Re: pgsql: Implement lazy XID allocation: transactions that do not modify

On 9/5/2007 2:10 PM, Tom Lane wrote:
> Log Message:
> -----------
> Implement lazy XID allocation: transactions that do not modify any database
> rows will normally never obtain an XID at all.  We already did things this way

As a side note, this patch is transparent enough that it doesn't seem to
affect even Slony replication, which makes excessive use of transaction
ID's and snapshot information to decide which log rows to apply together
in order to guarantee consistency on subscribers at all times.

Good Job!


Jan


> for subtransactions, but this patch extends the concept to top-level
> transactions.  In applications where there are lots of short read-only
> transactions, this should improve performance noticeably; not so much from
> removal of the actual XID-assignments, as from reduction of overhead that's
> driven by the rate of XID consumption.  We add a concept of a "virtual
> transaction ID" so that active transactions can be uniquely identified even
> if they don't have a regular XID.  This is a much lighter-weight concept:
> uniqueness of VXIDs is only guaranteed over the short term, and no on-disk
> record is made about them.
>
> Florian Pflug, with some editorialization by Tom.
>
> Modified Files:
> --------------
>     pgsql/doc/src/sgml:
>         catalogs.sgml (r2.156 -> r2.157)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/catalogs.sgml?r1=2.156&r2=2.157)
>         config.sgml (r1.141 -> r1.142)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.141&r2=1.142)
>     pgsql/src/backend/access/heap:
>         heapam.c (r1.237 -> r1.238)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c?r1=1.237&r2=1.238)
>     pgsql/src/backend/access/transam:
>         README (r1.6 -> r1.7)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/README?r1=1.6&r2=1.7)
>         clog.c (r1.43 -> r1.44)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/clog.c?r1=1.43&r2=1.44)
>         multixact.c (r1.24 -> r1.25)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/multixact.c?r1=1.24&r2=1.25)
>         twophase.c (r1.32 -> r1.33)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase.c?r1=1.32&r2=1.33)
>         xact.c (r1.247 -> r1.248)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xact.c?r1=1.247&r2=1.248)
>         xlog.c (r1.279 -> r1.280)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.279&r2=1.280)
>     pgsql/src/backend/catalog:
>         system_views.sql (r1.41 -> r1.42)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/system_views.sql?r1=1.41&r2=1.42)
>     pgsql/src/backend/commands:
>         indexcmds.c (r1.162 -> r1.163)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/indexcmds.c?r1=1.162&r2=1.163)
>         sequence.c (r1.143 -> r1.144)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/sequence.c?r1=1.143&r2=1.144)
>         vacuum.c (r1.355 -> r1.356)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c?r1=1.355&r2=1.356)
>         vacuumlazy.c (r1.90 -> r1.91)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c?r1=1.90&r2=1.91)
>     pgsql/src/backend/storage/ipc:
>         procarray.c (r1.28 -> r1.29)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/procarray.c?r1=1.28&r2=1.29)
>         sinvaladt.c (r1.63 -> r1.64)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/sinvaladt.c?r1=1.63&r2=1.64)
>     pgsql/src/backend/storage/lmgr:
>         lmgr.c (r1.92 -> r1.93)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lmgr.c?r1=1.92&r2=1.93)
>         lock.c (r1.177 -> r1.178)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lock.c?r1=1.177&r2=1.178)
>         proc.c (r1.192 -> r1.193)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/proc.c?r1=1.192&r2=1.193)
>     pgsql/src/backend/storage/smgr:
>         smgr.c (r1.105 -> r1.106)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/smgr/smgr.c?r1=1.105&r2=1.106)
>     pgsql/src/backend/utils/adt:
>         lockfuncs.c (r1.28 -> r1.29)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/lockfuncs.c?r1=1.28&r2=1.29)
>     pgsql/src/backend/utils/error:
>         elog.c (r1.195 -> r1.196)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c?r1=1.195&r2=1.196)
>     pgsql/src/backend/utils/misc:
>         postgresql.conf.sample (r1.225 -> r1.226)
>
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.225&r2=1.226)
>     pgsql/src/include/access:
>         xact.h (r1.88 -> r1.89)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xact.h?r1=1.88&r2=1.89)
>         xlog.h (r1.82 -> r1.83)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xlog.h?r1=1.82&r2=1.83)
>     pgsql/src/include:
>         c.h (r1.220 -> r1.221)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/c.h?r1=1.220&r2=1.221)
>     pgsql/src/include/catalog:
>         catversion.h (r1.422 -> r1.423)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.422&r2=1.423)
>     pgsql/src/include/storage:
>         lmgr.h (r1.58 -> r1.59)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lmgr.h?r1=1.58&r2=1.59)
>         lock.h (r1.106 -> r1.107)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lock.h?r1=1.106&r2=1.107)
>         proc.h (r1.99 -> r1.100)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/proc.h?r1=1.99&r2=1.100)
>         procarray.h (r1.14 -> r1.15)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/procarray.h?r1=1.14&r2=1.15)
>         sinvaladt.h (r1.42 -> r1.43)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/sinvaladt.h?r1=1.42&r2=1.43)
>         smgr.h (r1.58 -> r1.59)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/smgr.h?r1=1.58&r2=1.59)
>     pgsql/src/test/regress/expected:
>         rules.out (r1.131 -> r1.132)
>         (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/rules.out?r1=1.131&r2=1.132)
>
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