pgsql: Allow read only connections during recovery, known as Hot

Log Message:
-----------
Allow read only connections during recovery, known as Hot Standby.

Enabled by recovery_connections = on (default) and forcing archive recovery using a recovery.conf. Recovery processing
nowemulates the original transactions as they are replayed, providing full locking and MVCC behaviour for read only
queries.Recovery must enter consistent state before connections are allowed, so there is a delay, typically short,
beforeconnections succeed. Replay of recovering transactions can conflict and in some cases deadlock with queries
duringrecovery; these result in query cancellation after max_standby_delay seconds have expired. Infrastructure changes
haveminor effects on normal running, though introduce four new types of WAL record.  

New test mode "make standbycheck" allows regression tests of static command behaviour on a standby server while in
recovery.Typical and extreme dynamic behaviours have been checked via code inspection and manual testing. Few port
specificbehaviours have been utilised, though primary testing has been on Linux only so far.  

This commit is the basic patch. Additional changes will follow in this release to enhance some aspects of behaviour,
notablyimproved handling of conflicts, deadlock detection and query cancellation. Changes to VACUUM FULL are also
required.

Simon Riggs, with significant and lengthy review by Heikki Linnakangas, including streamlined redesign of snapshot
creationand two-phase commit. 

Important contributions from Florian Pflug, Mark Kirkwood, Merlin Moncure, Greg Stark, Gianni Ciolli, Gabriele
Bartolini,Hannu Krosing, Robert Haas, Tatsuo Ishii, Hiroyuki Yamada plus support and feedback from many other community
members.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        backup.sgml (r2.130 -> r2.131)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/backup.sgml?r1=2.130&r2=2.131)
        config.sgml (r1.238 -> r1.239)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.238&r2=1.239)
        func.sgml (r1.493 -> r1.494)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml?r1=1.493&r2=1.494)
    pgsql/doc/src/sgml/ref:
        checkpoint.sgml (r1.16 -> r1.17)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/checkpoint.sgml?r1=1.16&r2=1.17)
    pgsql/src/backend/access/gin:
        ginxlog.c (r1.19 -> r1.20)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginxlog.c?r1=1.19&r2=1.20)
    pgsql/src/backend/access/gist:
        gistxlog.c (r1.32 -> r1.33)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gist/gistxlog.c?r1=1.32&r2=1.33)
    pgsql/src/backend/access/heap:
        heapam.c (r1.278 -> r1.279)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c?r1=1.278&r2=1.279)
        pruneheap.c (r1.18 -> r1.19)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/pruneheap.c?r1=1.18&r2=1.19)
    pgsql/src/backend/access/index:
        genam.c (r1.77 -> r1.78)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/index/genam.c?r1=1.77&r2=1.78)
        indexam.c (r1.115 -> r1.116)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/index/indexam.c?r1=1.115&r2=1.116)
    pgsql/src/backend/access/nbtree:
        README (r1.20 -> r1.21)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/README?r1=1.20&r2=1.21)
        nbtinsert.c (r1.174 -> r1.175)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtinsert.c?r1=1.174&r2=1.175)
        nbtpage.c (r1.113 -> r1.114)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtpage.c?r1=1.113&r2=1.114)
        nbtree.c (r1.172 -> r1.173)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtree.c?r1=1.172&r2=1.173)
        nbtxlog.c (r1.55 -> r1.56)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/nbtree/nbtxlog.c?r1=1.55&r2=1.56)
    pgsql/src/backend/access/transam:
        README (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/README?r1=1.12&r2=1.13)
        clog.c (r1.53 -> r1.54)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/clog.c?r1=1.53&r2=1.54)
        multixact.c (r1.32 -> r1.33)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/multixact.c?r1=1.32&r2=1.33)
        recovery.conf.sample (r1.4 -> r1.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/recovery.conf.sample?r1=1.4&r2=1.5)
        rmgr.c (r1.27 -> r1.28)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/rmgr.c?r1=1.27&r2=1.28)
        subtrans.c (r1.24 -> r1.25)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/subtrans.c?r1=1.24&r2=1.25)
        twophase.c (r1.56 -> r1.57)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase.c?r1=1.56&r2=1.57)
        twophase_rmgr.c (r1.10 -> r1.11)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase_rmgr.c?r1=1.10&r2=1.11)
        xact.c (r1.277 -> r1.278)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xact.c?r1=1.277&r2=1.278)
        xlog.c (r1.353 -> r1.354)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.353&r2=1.354)
    pgsql/src/backend/commands:
        dbcommands.c (r1.228 -> r1.229)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/dbcommands.c?r1=1.228&r2=1.229)
        lockcmds.c (r1.25 -> r1.26)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/lockcmds.c?r1=1.25&r2=1.26)
        sequence.c (r1.162 -> r1.163)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/sequence.c?r1=1.162&r2=1.163)
        tablespace.c (r1.63 -> r1.64)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/tablespace.c?r1=1.63&r2=1.64)
        vacuum.c (r1.398 -> r1.399)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c?r1=1.398&r2=1.399)
        vacuumlazy.c (r1.124 -> r1.125)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c?r1=1.124&r2=1.125)
    pgsql/src/backend/postmaster:
        postmaster.c (r1.596 -> r1.597)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c?r1=1.596&r2=1.597)
    pgsql/src/backend/storage/ipc:
        Makefile (r1.22 -> r1.23)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/Makefile?r1=1.22&r2=1.23)
        procarray.c (r1.51 -> r1.52)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/procarray.c?r1=1.51&r2=1.52)
        sinvaladt.c (r1.79 -> r1.80)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/sinvaladt.c?r1=1.79&r2=1.80)
    pgsql/src/backend/storage/lmgr:
        README (r1.24 -> r1.25)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/README?r1=1.24&r2=1.25)
        lock.c (r1.188 -> r1.189)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/lock.c?r1=1.188&r2=1.189)
        proc.c (r1.209 -> r1.210)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/lmgr/proc.c?r1=1.209&r2=1.210)
    pgsql/src/backend/tcop:
        postgres.c (r1.578 -> r1.579)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.578&r2=1.579)
        utility.c (r1.324 -> r1.325)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/utility.c?r1=1.324&r2=1.325)
    pgsql/src/backend/utils/adt:
        txid.c (r1.8 -> r1.9)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/txid.c?r1=1.8&r2=1.9)
        xid.c (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/xid.c?r1=1.12&r2=1.13)
    pgsql/src/backend/utils/cache:
        inval.c (r1.89 -> r1.90)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/inval.c?r1=1.89&r2=1.90)
    pgsql/src/backend/utils/error:
        elog.c (r1.219 -> r1.220)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c?r1=1.219&r2=1.220)
    pgsql/src/backend/utils/init:
        postinit.c (r1.198 -> r1.199)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/init/postinit.c?r1=1.198&r2=1.199)
    pgsql/src/backend/utils/misc:
        guc.c (r1.527 -> r1.528)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.527&r2=1.528)
        postgresql.conf.sample (r1.271 -> r1.272)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.271&r2=1.272)
    pgsql/src/backend/utils/time:
        snapmgr.c (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/snapmgr.c?r1=1.12&r2=1.13)
        tqual.c (r1.113 -> r1.114)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/time/tqual.c?r1=1.113&r2=1.114)
    pgsql/src/bin/pg_controldata:
        pg_controldata.c (r1.44 -> r1.45)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_controldata/pg_controldata.c?r1=1.44&r2=1.45)
    pgsql/src/include:
        miscadmin.h (r1.215 -> r1.216)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/miscadmin.h?r1=1.215&r2=1.216)
    pgsql/src/include/access:
        heapam.h (r1.144 -> r1.145)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/heapam.h?r1=1.144&r2=1.145)
        htup.h (r1.107 -> r1.108)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/htup.h?r1=1.107&r2=1.108)
        nbtree.h (r1.125 -> r1.126)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/nbtree.h?r1=1.125&r2=1.126)
        relscan.h (r1.67 -> r1.68)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/relscan.h?r1=1.67&r2=1.68)
        rmgr.h (r1.19 -> r1.20)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/rmgr.h?r1=1.19&r2=1.20)
        subtrans.h (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/subtrans.h?r1=1.12&r2=1.13)
        transam.h (r1.70 -> r1.71)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/transam.h?r1=1.70&r2=1.71)
        twophase.h (r1.12 -> r1.13)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/twophase.h?r1=1.12&r2=1.13)
        twophase_rmgr.h (r1.9 -> r1.10)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/twophase_rmgr.h?r1=1.9&r2=1.10)
        xact.h (r1.98 -> r1.99)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xact.h?r1=1.98&r2=1.99)
        xlog.h (r1.93 -> r1.94)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xlog.h?r1=1.93&r2=1.94)
        xlog_internal.h (r1.25 -> r1.26)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/xlog_internal.h?r1=1.25&r2=1.26)
    pgsql/src/include/catalog:
        pg_control.h (r1.44 -> r1.45)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_control.h?r1=1.44&r2=1.45)
        pg_proc.h (r1.556 -> r1.557)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.556&r2=1.557)
    pgsql/src/include/storage:
        lock.h (r1.116 -> r1.117)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/lock.h?r1=1.116&r2=1.117)
        proc.h (r1.114 -> r1.115)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/proc.h?r1=1.114&r2=1.115)
        procarray.h (r1.26 -> r1.27)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/procarray.h?r1=1.26&r2=1.27)
        sinval.h (r1.53 -> r1.54)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/sinval.h?r1=1.53&r2=1.54)
        sinvaladt.h (r1.51 -> r1.52)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/sinvaladt.h?r1=1.51&r2=1.52)
    pgsql/src/include/utils:
        builtins.h (r1.341 -> r1.342)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h?r1=1.341&r2=1.342)
        snapshot.h (r1.5 -> r1.6)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/snapshot.h?r1=1.5&r2=1.6)
    pgsql/src/test/regress:
        GNUmakefile (r1.80 -> r1.81)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/GNUmakefile?r1=1.80&r2=1.81)
        pg_regress.c (r1.67 -> r1.68)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.c?r1=1.67&r2=1.68)

Added Files:
-----------
    pgsql/src/backend/storage/ipc:
        standby.c (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/standby.c?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/include/storage:
        standby.h (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/standby.h?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/test/regress:
        standby_schedule (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/standby_schedule?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/test/regress/expected:
        hs_standby_allowed.out (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/hs_standby_allowed.out?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_check.out (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/hs_standby_check.out?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_disallowed.out (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/hs_standby_disallowed.out?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_functions.out (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/hs_standby_functions.out?rev=1.1&content-type=text/x-cvsweb-markup)
    pgsql/src/test/regress/sql:
        hs_primary_extremes.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/hs_primary_extremes.sql?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_primary_setup.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/hs_primary_setup.sql?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_allowed.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/hs_standby_allowed.sql?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_check.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/hs_standby_check.sql?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_disallowed.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/hs_standby_disallowed.sql?rev=1.1&content-type=text/x-cvsweb-markup)
        hs_standby_functions.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/hs_standby_functions.sql?rev=1.1&content-type=text/x-cvsweb-markup)