Re: 7.3 schedule - Mailing list pgsql-hackers

On Fri, Apr 12, 2002 at 12:41:34AM -0400, Neil Conway wrote:
> On Fri, 12 Apr 2002 12:58:01 +0900
> "Hiroshi Inoue" <Inoue@tpf.co.jp> wrote:
> > 
> > Just a confirmation.
> > Someone is working on PREPARE/EXECUTE ?
> > What about Karel's work ?
Right question :-)
> I am. My work is based on Karel's stuff -- at the moment I'm still
> basically working on getting Karel's patch to play nicely with
> current sources; once that's done I'll be addressing whatever
> issues are stopping the code from getting into CVS.
My patch (qcache) for PostgreSQL 7.0 is available at ftp://ftp2.zf.jcu.cz/users/zakkr/pg/.I very look forward to Neil's
workon this. 
 
Notes:
   * It's experimental patch, but usable. All features below mentioned      works.
   * PREPARE/EXECUTE is not only SQL statements, I think good idea is     create something common and robus for
query-plancaching,     beacuse there is for example SPI too. The RI triggers are based      on SPI_saveplan().    * My
patchknows EXECUTE INTO feature:
 
PREPARE foo AS SELECT * FROM pg_class WHERE relname ~~ $1 USING text;
EXECUTE foo USING 'pg%';        <-- standard select
EXECUTE foo INTO TEMP newtab USING 'pg%';  <-- select into   * The patch allows store query-planns to shared memory and
is    possible EXECUTE it at more backends (over same DB) and planns     are persistent across connetions. For this
featureI create special      memory context subsystem (like current aset.c, but it works with      IPC shared memory).
       This is maybe too complex solution and (maybe) sufficient is cache      query in one backend only. I know
unbeliefabout this shared     memory solution (Tom?).            Karel          My experimental patch README (excuse my
English):
Implementation~~~~~~~~~~~~~~
  The qCache allows save queryTree and queryPlan. There is available are   two space for data caching.    LOCAL  - data
arecached in backend non-shared memory and data aren't           available in other backends.                     SHARE
- data are cached in backend shared memory and data are            visible in all backends.   Because size of share
memorypool is limited and it is set during  postmaster start up, the qCache must remove all old planns if pool is
full.You can mark each entry as "REMOVEABLE" or "NOTREMOVEABLE".    A removeable entry is removed if pool is full.   A
not-removeableentry must be removed via qCache_Remove() or   the other routines. The qCache not remove this entry
itself.  All records in qCache are cached (in the hash table) under some key.  The qCache knows two alternate of key
---"KEY_STRING" and "KEY_BINARY".    The qCache API not allows access to shared memory, all cached planns that   API
returnsare copy to CurrentMemoryContext. All (qCache_ ) routines lock   shmem itself (exception is
qCache_RemoveOldest_ShareRemoveAble()).
       - for locking is used spin lock.
  Memory management  ~~~~~~~~~~~~~~~~~  The qCache use for qCache's shared pool its memory context independent on
standardaset/mcxt, but use compatible API --- it allows to use standard  palloc() (it is very needful for basic
plan-treeoperations, an example   for copyObject()). The qCache memory management is very simular to current  aset.c
code.It is chunk-ed blocks too, but the block is smaller - 1024b.
 
  The number of blocks is available set in postmaster 'argv' via option  '-Z'.
  For plan storing is used separate MemoryContext for each plan, it   is good idea (Hiroshi's ?), bucause create new
contextis simple and   inexpensive and allows easy destroy (free) cached plan. This method is   used in my SPI overhaul
insteadTopMemoryContext feeding.
 
  Postmaster  ~~~~~~~~~~  The query cache memory is init during potmaster startup. The size of  query cache pool is set
via'-Z <number-of-blocks>' switch --- default   is 100 blocks where 1 block = 1024b, it is sufficient for 20-30 cached
planns.One query needs somewhere 3-10 blocks, for example query like
 
       PREPARE sel AS SELECT * FROM pg_class;
  needs 10Kb, because table pg_class has very much columns.   Note: for development I add SQL function: "SELECT
qcache_state();",       this routine show usage of qCache.
 
SPI~~~   I a little overwrite SPI save plan method and remove TopMemoryContext   "feeding".
   Standard SPI:
       SPI_saveplan() - save each plan to separate standard memory context.
       SPI_freeplan() - free plan.
   By key SPI:
       It is SPI interface for query cache and allows save planns to SHARED       or LOCAL cache 'by' arbitrary key
(stringor binary). Routines:
 
       SPI_saveplan_bykey()    - save plan to query cache
       SPI_freeplan_bykey()    - remove plan from query cache
       SPI_fetchplan_bykey()   - fetch plan saved in query cache
       SPI_execp_bykey()       - execute (via SPI) plan saved in query                                 cache 
       - now, users can write functions that save planns to shared memory        and planns are visible in all backend
andare persistent arcoss        connection. 
 
       Example:       ~~~~~~~       /* ----------        * Save/exec query from shared cache via string key        *
----------       */       int     keySize = 0;                       flag = SPI_BYKEY_SHARE | SPI_BYKEY_STRING;
char   *key = "my unique key";              res = SPI_execp_bykey(values, nulls, tcount, key, flag, keySize);
  if (res == SPI_ERROR_PLANNOTFOUND)        {               /* --- not plan in cache - must create it --- */
                 void *plan;
 
               plan = SPI_prepare(querystr, valnum, valtypes);               SPI_saveplan_bykey(plan, key, keySize,
flag);                             res = SPI_execute(plan, values, Nulls, tcount);       }              elog(NOTICE,
"Processed:%d", SPI_processed);
 

PREPARE/EXECUTE~~~~~~~~~~~~~~~  * Syntax:              PREPARE <name> AS <query>                [ USING type, ... typeN
]               [ NOSHARE | SHARE | GLOBAL ]              EXECUTE <name>                [ INTO [ TEMPORARY | TEMP ] [
TABLE] new_table ]               [ USING val, ... valN ]                      [ NOSHARE | SHARE | GLOBAL ]
 
       DEALLOCATE PREPARE                [ <name> [ NOSHARE | SHARE | GLOBAL ]]               [ ALL | ALL INTERNAL ]

    I know that it is a little out of SQL92... (use CREATE/DROP PLAN instead    this?) --- what mean SQL standard
guru?
  * Where:       NOSHARE --- cached in local backend query cache - not accessable                   from the others
backendsand not is persisten a across                   conection.
 
       SHARE   --- cached in shared query cache and accessable from                   all backends which work over same
database.
       GLOBAL  --- cached in shared query cache and accessable from                   all backends and all databases. 
       - default is 'SHARE'         Deallocate:                              ALL          --- deallocate all users's
plans
               ALL INTERNAL --- deallocate all internal plans, like planns                                cached via
SPI.It is needful if user                                alter/drop table ...etc.
 
  * Parameters:              "USING" part in the prepare statement is for datetype setting for       paremeters in the
query.For example:
 
       PREPARE sel AS SELECT * FROM pg_class WHERE relname ~~ $1 USING text;
       EXECUTE sel USING 'pg%';       
  * Limitation:              - prepare/execute allow use full statement of SELECT/INSERT/DELETE/         UPDATE.
-possible is use union, subselects, limit, ofset, select-into
 

Performance:~~~~~~~~~~~* the SPI
       - I for my tests a little change RI triggers to use SPI by_key API       and save planns to shared qCache
insteadto internal RI hash table.
 
       The RI use very simple (for parsing) queries and qCache interest is        not visible. It's better if backend
veryoften startup and RI check        always same tables. In this situation speed go up --- 10-12%.        (This
snapshotnot include this RI change.)
 
       But all depend on how much complicate for parser is query in        trigger.
* PREPARE/EXECUTE              - For tests I use query that not use some table (the executor is        in boredom
state),but is difficult for the parser. An example:
 
       SELECT 'a text ' || (10*10+(100^2))::text || ' next text ' || cast        (date_part('year', timestamp 'now') AS
text);                        - (10000 * this query):
 
       standard select:        54 sec       via prepare/execute:     4 sec   (93% better)
       IMHO it is nod bad.       - For standard query like:
       SELECT u.usename, r.relname FROM pg_class r, pg_user u WHERE        r.relowner = u.usesysid;
       it is with PREPARE/EXECUTE 10-20% faster.

-- Karel Zak  <zakkr@zf.jcu.cz>http://home.zf.jcu.cz/~zakkr/C, PostgreSQL, PHP, WWW, http://docs.linux.cz,
http://mape.jcu.cz