Showplan显示SQL最终的执行过程，用了什么index，什么合并算法等。 dbcc traceon(302) 可以帮我们找出为什么optimizer。
dbcc traceon的输出非常详细，比showplan详细的多。
启用/关闭dbcc trace
在isql里运行一下命令
>>>dbcc traceon(3604, 302)
>>>dbcc
traceoff(3604, 302)
3604 表示 Directs trace output to the client, rather
than to the error log.
302表示 Prints trace information on index selection.
dbcc traceon(310)
provides more detail on the optimizer’s join order decisions and final cost estimates.
dbcc traceon(310) also prints a “Final plan” block at the end of query optimization.
启用/关闭dbcc trace(310)
>>>dbcc traceon(3604, 302, 310)
>>>dbcc traceoff(3604, 302, 310)
dbcc traceon(302) 输出的结构
优化程序对查询中所涉及的各表的子句进行检查时， dbcc traceon(302)显示其输出。优化程序首先检查所有的搜索子句，并为查询中每个表的搜索子句确定各种可能访问方法的开销。然后检查各个连接子句和连接可用索引的开销。
dbcc traceon(302) 将每个搜索和连接分析作为输出块输出，并以一行星号分隔。
搜索和连接块各自包含更小的信息块：
· 表信息块，给出表中的基本信息
· 显示表扫描开销的块
· 显示被分析的子句的块
· 每个被分析索引的块
· 显示该部分子句的最佳索引的块
对于连接，每种连接顺序都由一个独立的块来代表。例如，对于
titles、titleauthor 和 authors 上的连接：
where titles.title_id = titleauthor.title_id
and authors.au_id = titleauthor.au_id
下面所示是一个每个连接都有的块：
· titles、titleauthor
· titleauthor、titles
· titleauthor、authors
· authors、titleauthor
dbcc sqltext(spid) 通过进程ID找出当前该进程正在运行的SQL
dbcc traceflags(1 or 2) 查看哪些traceflag被开启了
已知的Traceflag
100 Display a parse tree for each command 108 Allow dynamic and host variables in create view statements 116 Print the text of the abstract query plan. Supported by Sybase, see documentation 200 Display messages about the before image of the query-tree 201 Display messages about the after image of the query tree 208 Show types of locks taken 217 Display a warning message for using the T-SQL extension of queries with grouped aggregates and columns in the select list which are not in the GROUP BY clause. 241 Compress all query-trees when ASE is started 243 Do not expand select * to column names when creating a compiled object 244 When set, the maximum length of the returned value of str_replace() is 16384, otherwise it is 255 260 Reduce TDS (Tabular Data Stream) overhead in stored procedures. Turn off done-in-behaviour packets. See also Send doneinproc tokens. 291 Changes the hierarchy and casting of datatypes to pre-11.5.1 behaviour. There was an issue is some very rare cases where a wrong result could occur, but that's been cleared up in 11.9.2 and above. 292 Never send doneinproc tokens. See also Send doneinproc tokens. 298 Display an error message when a query uses a correlated variable as an inner or outer member of an outer join. 299 Do not recompile a stored procedure that inherits a temp table from a parent procedure. 302 Print trace information on index selection, supported by Sybase, see documentation 303 Display optimizer OR strategy 304 Revert special "or" optimizer strategy to the strategy used in pre-System 11 (this traceflag resolved several bug issues in System 11, most of these bugs are fixed in ASE 11.0.3.2) 310 Show the plan as choosen by the optimizer, as well as I/O costs. Supported by Sybase see documentation 311 Display optimizers expected I/O cost 317 Show all considered plans. Supported by Sybase, see documentation 319 Display optimizer reformatting strategy 320 Turn off join order heuristics 321 Display optimizers reformatting strategy briefly 324 Turn off the like optimization for ad-hoc queries using local variables 326 Instructs the server to use arithmetic averaging when calculating density instead of a geometric weighted average when updating statistics. Useful for building better stats when an index has skew on the leading column. Use only for updating the stats of a table/index with known skewed data. 329 Turns on a strategy for fast first row return for queries using cursors with an ORDERBY. 333 Disables min-max optimization 334 Enable merge joins 353 Turn off transitive closure 362 Will disable delta project 364 Use range density instead of total density 370 Use min-max index as an alternative to the table scan for single table queries. Does not perform aggregation optimization for joins. 384 Enable JTC 396 Use min-max optimization for single table queries. 450 Sort a group by operation in the order of the groups 516 Print mapping between xchg operators and worker processes when using parallel execution. Supported by Sybase, see documentation 526 Print semi-graphical execution operator tree when showplan is enabled. Supported by Sybase, see documentation 589 Close a cursor implicitly during a cursor fetch and after an error was hit. 602 Prints out diagnostic information for deadlock prevention. 603 Prints out diagnostic information when avoiding deadlock. 615 When a read of a page does not indicate it's right identity a second read is done. When the identity is now correct the related device is suspect and ASE turns on additional diagnostic checks. The check can be turned off with the traceflag. 646 Turn off the new space allocation method as introduced in 12.5.3 for partitioned DOL tables 693 Turn off some blocking optimizations in scans such as skipping uncommitted inserts and skipping or returning uncommitted updates based on info about what columns were updated. 695 Turn off update_mode optimization completely for multi-row updates (bugfix 97199) 699 Turn off transaction logging 712 Disable procedure cache optimisation 712 Turn off engine local memory optimization. Engine local cache enhancements were added to ASE, and disabling this should not make a noticeable impact on ASE servers running with less than 5 engines. (no benchmarks). (see case 11270180) 720 disable the warning msg "memory usage in procedure headers XXX does not match memory usage count in Pss (XXXX) for server process id XXXX." This error is reported when Adaptive Server cleans up after normal completion of a batch process and determines that the memory usage tracked by the procedure header does not match the usage total maintained in the PSS. No action is required, since this is an informational message and does not result in any incorrect behavior. Upon detecting the memory count mismatch, Adaptive Server corrects the appropriate counter, completes the cleanup tasks, and continues processing. (available since ASE 12.0.0.4 ESD#1) 722 ASE (debug version) will perform additional checks on the heap memory to detect possible memory corruption. 833 Do not report Msg 880 "Your query is blocked because it tried to write and database '' is in quiesce state. Your query will proceed after the DBA performs QUIESCE DATABASE RELEASE.". 990 Allow only access to the server with the "sa" account. Supported by Sybase, see documentation 1116 Suppress Msg 1131. (The OAM page does not belong to object with index.....) 1202 Also show the blocked lock requests in master..syslocks 1204 Print deadlock information into errorlog 1205 Prints deadlock information by printing stacktraces. 1206 Disable lock promotion. 1212 Shows info about locks granted and released 1213 Used with dbcc object_stats 1217 Show info about locks being acquired 1603 Turns off async i/o and forces standard unix io. Can be useful if symptoms include transient corruption errors that may be caused by bad drives or controllers. 1605 Start secondary engines by hand 1606 Create a debug engine start file. This allows you to start up a debug engine which can access the server's shared memory for running diagnostics. 1608 Instructs server engine 0 to not on-line any other dataserver engines 1610 Boot the server with TCP_NODELAY enabled. 1611 If possible, pin shared memory -- check errorlog for success/failure. 1613 Set affinity of the ASE engine's onto particular CPUs usually pins engine 0 to processor 0, engine 1 to processor 1, etc 1615 SGI only: turn on recoverability to filesystem devices. 1625 Linux only: Revert to using cached filesystem I/O. By default, ASE on Linux opens filesystem devices using O_SYNC, unlike other Unix based releases, which means it is safe to use filesystems devices for production systems. 1630 SuSE 32 bit Linux (SuSE 9 SP1 or later), ASE incorrectly identifies AIO to be KAIO while using Posix AIO. Can lead to ASE hang. Start with this trace flag. 1642 Reserve one third of the sockets for EJB. 1649 Allow the server to run Linux Kernel Async I/O. For Linux kernel 2.6 and above, to force low level kernel async I/O. 1650 Allow copying encrypted password strings between platforms (e.g. Solaris to Linux) 2205 Show HA debugging output, supported by Sybase see documentation 2209 Used when upgrading ASE configured with high availability 2512 Instructs dbcc checkalloc to skip the syslogs table during processing. 2513 Instructs dbcc checkalloc, tablealloc and indexalloc to check for whether foreign objects are stranded on a particular segment within a database. Supported by Sybase, see documentation 2703 When using update statistics with sampling and the index/column does not have existing statistics, set join density and total density to values from the sample rather then to defaults. 3100 Load a database even when the characterset or sort order of a dump file is incompatible with the server. 3199 When ONLINE DATABASE fails with Msg 2610 (Could not find leaf row in nonclustered index partition ...) after a cross-platform database load, set the traceflag on, reload the dump and online again. 3300 Display each log record that is being processed during recovery. You may wish to redirect stdout because it can be a lot of information. 3453 During the redo pass, allow the page timestamp to fall between the log old timestamp and the log new timestamp and also for the page timestamp to be behind the log old timestamp. In such cases, fix up the page timestamp to be the log old timestamp so that the current log record will be redone. Used to compensate for bugs in the recovery of sort. This trace flag MUST only be used in exceptional cases, and only where it is known that modifying the page timestamp is the correct thing to do. If not used wisely, data corruptions can occur. (see case 11159541) 3474 Disable tuning of buffer pools on recovery 3500 Disable checkpointing. 3502 Write an entry in the errorlog when a databases is checkpointed 3504 For internal testing. Will raise a bogus log-out-of-space condition from checkpoint() 3601 Write a stacktrace to the errorlog every time an error is raised. 3604 Send trace output to the session of the client. Supported by Sybase see documentation 3605 Send trace output to the errorlog of the server. Supported by Sybase see documentation 3607 Do not start recovery when booting ASE. 3608 Recover only the master database. Do not clear tempdb or start up checkpoint process. 3609 Recover all databases. Do not clear tempdb or start up checkpoint process. 3610 Pre-System 10 behaviour: divide by zero to result in NULL instead of error 3620 Do not kill infected processes. 3635 Print diagnostic information (see case 11257124, to get info for LDAP login problem). Trace Flag 3635 Diagnostics are written to the console that started ASE. There are not written to the errorlog, even if 3605 is turned on. 3706 Performance improvement of drop table in tempdb. 3708 By default ASE (12.5.3 onwards) will release the system catalog locks during the drop of user tables in tempdb when not in DDL-IN-TRAN mode after the commit of the transaction but before post commit work started. Turns off the default behaviour 3710 Improve the performance of DROP INDEX and CREATE INDEX by releasing the system catalog locks when not in DDL-IN-TRAN mode after the commit of the transaction but before post commit work started. 4001 Display a message in the errorlog when a loginrecord is recieved 4012 Don't spawn chkptproc. 4013 Write a message to the errorlog when a login takes place. 4020 Boot without recover. 4044 Allows to log into ASE when the "sa" login is locked 4063 used by 12.0 server to turn on sqldbgr RPCs 4066 Turn off the check for invalid data being sent from a connecting client. (see case 11239779: After ugraded to ASE 1253 to 1251, getting errors when logging into application: The packet size (0) specified at login time is illegal. Legal values are between 512 and 512.) 4072 Disable the global login trigger 4073 Export the result of certain "set" command within a login trigger to the session. 4080 When an UPDATE using tsequal() is done within a stored procedure, tsequal() no longer returns a timestamp value unless the trace flag is set. 4404 to disable pushdown of Union views. Change the order of the union view and the other view in the from clause, so that the union view is the last entry in the from clause 4413 Trace queries in a 12.5 server that are join-order dependent. 4419 In some cases, outer join on view or derived table with CASE expression may perform slower due to view materialization.The workaround is to use traceflag 4419. 5303 Select into a temporary table will be executed without the table being sliced 5304 Disable the large I/O and large allocation changes done under 279883-1. 5101 Forces all I/O requests to go through engine 0. This removes the contention between processors but could create a bottleneck if engine 0 becomes busy with non-I/O tasks. 5102 Prevents engine 0 from running any non-affinitied tasks. 7103 Disable table lock promotion for text columns. 7408 Force the server to scan *log segment* allocation pages; to recalculate free log space rather than use saved counts at boot time. (see case 11195087) 7409 Force the server to scan *data* segment allocation pages; to recalculate free data page space rather than use saved counts at boot time. (see case 11195087) 7703 When assinging a value from a table into a local variable, go through the whole resultset rather than jump to last row and assing the value once. 7709 In 12.5.2, an insert inside a stored proc writes trailing white space when selecting from a char not null field. This can lead to strange results when when selecting data. The traceflag disables this padding. 7717 Disable check of client compatibility in ASE 15. See Version 15 client compatibility 7738 Support plan sharing of cached statements across different users. 7815 logs address connection requests and host / name lookups. 7824 Disable the master/query syntax in the interfaces file 7841 Make ASE IPv6 aware 7844 Enable/disable concurrent Kerberos authentication 8003 prints info on RPC calls 8203 Display statement and transaction locks on a deadlock error. 8399 Instructs the dbcc monitor command to insert a valid description into the field_name column in the sysmonitors table. Not intended for use by users. Appears in the errorlog when sp_sysmon is used. 9217 When set, RepAgent will not stop after reporting error 9289 due to an inconsistent log record found. Instead it will attempt to continue after reporting error 9290 in the error log. Supported by Sybase, see documentation 9531 Dump expensive buffer allocation analysis 10303 Invoke set completion of object ownership methodology and object resolution from old procedural ownership 11201 Logs client connect events, disconnect events, and attention events. Supported by Sybase, see documentation 11202 Logs client language, cursor declare, dynamic prepare, and dynamic execute-immediate text. Supported by Sybase, see documentation 11203 Logs client rpc events. Supported by Sybase, see documentation 11204 Logs all messages routed to client. Supported by Sybase, see documentation 11205 Logs all interaction with remote server. Supported by Sybase, see documentation 11206 Show messages about query processing for file access. Supported by Sybase, see documentation 11207 Log the processing of text and image datatypes from remote servers. Supported by Sybase, see documentation 11208 Prevents the create index and drop table statements from being transmitted to a remote server. sysindexes is updated anyway. Supported by Sybase, see documentation 11209 When running "update statistics" on remote tables update only the rowcount. Supported by Sybase, see documentation 11210 Disables Component Integration Services enhanced remote query optimization. 11211 Prevents the drop table syntax from being forwarded to remote servers if the table was created using the create table at location syntax. Supported by Sybase, see documentation 11212 Prevents escape on underscores in table names. Supported by Sybase, see documentation 11213 Prevents generation of column and table constraints. Supported by Sybase, see documentation 11214 Disables Component Integration Services recovery at start-up. Supported by Sybase, see documentation 11215 Sets enhanced remote optimization for servers of class db2. 11216 For the session, disables enhanced remote optimization. Supported by Sybase, see documentation 11217 For the server, disables enhanced remote optimization. Supported by Sybase, see documentation 11218 Any query that is part of a declare cursor command, and that references proxy tables, is read only by default. Supported by Sybase, see documentation 11220 Disables constraint checking of remote tables on the local server. This avoids duplicate checking. Setting this trace flag on ensures that queries are not rejected by the quickpass mode because of constraints. (spid) Supported by Sybase, see documentation 11221 Disables alter table commands to the remote server when ON. This allows users to modify type, length, and nullability of columns in a local table without changing columns in the remote table. Use trace flag 11221 with caution. It may lead to tables that are “out of sync.” (spid). Supported by Sybase, see documentation 11223 Disables proxy table index creation during create existing table or create proxy_table command execution. If this flag is set on, no index metadata is imported from the remote site referenced by the proxy table, and no indexes for the proxy table are created. This trace flag should be used with care and turned off when no longer necessary. (global) Supported by Sybase, see documentation 11228 A 2762 error, "CREATE TABLE command is not allowed within multiple statement transaction" may be reported when executing a SQL INSERT..SELECT from proxy table mapped to a RPC. This traceflag has to be turned on to allow CREATE TABLE command in the remote procedure (for the session) 11229 Use pre-12.5.3 behaviour to import statistics for proxy tables. Supported by Sybase, see documentation 11231 CIS: Connections to remote servers are not disconnected and remain engine affinitied until the client session terminates. The connections can now be dropped and detached from an engine after executing a statement to the remote server by enabling this flag. Exceptions are when the statement is participating in cursor, transaction or stored procedure operations; or when ASE is in either HA failover or failback states. 11232 A 2762 error, "CREATE TABLE command is not allowed within multiple statement transaction" may be reported when executing a SQL INSERT..SELECT from proxy table mapped to a RPC. This traceflag has to be turned on to allow CREATE TABLE command in the remote procedure (serverwide) 11299 Allows connection information to be logged when a connection to a remote server fails. Supported by Sybase, see documentation 11906 Informational messages from REORG will no longer be printed to the errorlog. 12628 Data insertion into DOL tables having nonclustered index will be done with the index prepend mode splits disabled, in order to improve disk space utilization. 15302 When a subquery appears in the ON clause of an outer join query, the performance may not be efficient. ASE will do optimization for subquery attachment to achieve more favorable performance when turned on. 15303 Possible performance improvement on a SELECT statement when a BIT column is involved in the WHERE clause. 15304 CR 422003: A SELECT statement using a LIKE clause with NULL variables returns Msg 712. Workaround for 'unable to allocate 0 bytes to heap' bug fixed in 12.5.3 ESD7. 15381 When set, the warning message 307, "Index specified as optimizer hint in the FROM clause of table does not exist. Optimizer will choose another index instead." is disabled. 15382 Disable "special OR strategy" (see release notes for the fine details) 15556 Allow dump and load in ASE cluster edition with multiple instances active