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  • Apache2 Segfault - need help interpreting this coredump (suspect cause is memcache / php session related)

    - by WayneDV
    Three Apache2 web servers running a PHP 5.2.3 web site. We're using Memcache to cache rendered pages but also as the storage engine of the PHP Sessions. At peak traffic times we're getting Apache segmentation faults on all three web servers and all HTTPD child processes segfault. My gut tells me that the increased Memcache traffic is stopping PHP sessions from being created or cleaned up and thus the processes die. Is it possible for someone to confirm that from the following? : #0 _zend_mm_free_int (heap=0x7fb67a075820, p=0x7fb67a011538) at /usr/src/debug/php-5.3.3/Zend/zend_alloc.c:2018 #1 0x00007fb665d02e82 in mmc_buffer_free (request=0x7fb67a011548) at /usr/src/debug/php-pecl-memcache-3.0.4/memcache-3.0.4/memcache_pool.c:50 #2 mmc_request_free (request=0x7fb67a011548) at /usr/src/debug/php-pecl-memcache-3.0.4/memcache-3.0.4/memcache_pool.c:169 #3 0x00007fb665d031ea in mmc_pool_free (pool=0x7fb67a00e458) at /usr/src/debug/php-pecl-memcache-3.0.4/memcache-3.0.4/memcache_pool.c:917 #4 0x00007fb665d0a2f1 in ps_close_memcache (mod_data=0x7fb66d625440) at /usr/src/debug/php-pecl-memcache-3.0.4/memcache-3.0.4/memcache_session.c:185 #5 0x00007fb66d1b0935 in php_session_save_current_state () at /usr/src/debug/php-5.3.3/ext/session/session.c:625 #6 php_session_flush () at /usr/src/debug/php-5.3.3/ext/session/session.c:1517 #7 0x00007fb66d1b0c1b in zm_deactivate_session (type=<value optimized out>, module_number=<value optimized out>) at /usr/src/debug/php-5.3.3/ext/session/session.c:2171 #8 0x00007fb66d2a719c in module_registry_cleanup (module=<value optimized out>) at /usr/src/debug/php-5.3.3/Zend/zend_API.c:2150 #9 0x00007fb66d2b1994 in zend_hash_reverse_apply (ht=0x7fb66d629d60, apply_func=0x7fb66d2a7180 <module_registry_cleanup>) at /usr/src/debug/php-5.3.3/Zend/zend_hash.c:755 #10 0x00007fb66d2a5c0d in zend_deactivate_modules () at /usr/src/debug/php-5.3.3/Zend/zend.c:866 #11 0x00007fb66d2541b5 in php_request_shutdown (dummy=<value optimized out>) at /usr/src/debug/php-5.3.3/main/main.c:1607 #12 0x00007fb66d32e037 in php_apache_request_dtor (r=0x7fb67a229658) at /usr/src/debug/php-5.3.3/sapi/apache2handler/sapi_apache2.c:509 #13 php_handler (r=0x7fb67a229658) at /usr/src/debug/php-5.3.3/sapi/apache2handler/sapi_apache2.c:681 #14 0x00007fb6784166f0 in ap_run_handler (r=0x7fb67a229658) at /usr/src/debug/httpd-2.2.15/server/config.c:158 #15 0x00007fb678419f58 in ap_invoke_handler (r=0x7fb67a229658) at /usr/src/debug/httpd-2.2.15/server/config.c:372 #16 0x00007fb6784254f0 in ap_process_request (r=0x7fb67a229658) at /usr/src/debug/httpd-2.2.15/modules/http/http_request.c:282 #17 0x00007fb678422418 in ap_process_http_connection (c=0x7fb67a2193a8) at /usr/src/debug/httpd-2.2.15/modules/http/http_core.c:190 #18 0x00007fb67841e1b8 in ap_run_process_connection (c=0x7fb67a2193a8) at /usr/src/debug/httpd-2.2.15/server/connection.c:43 #19 0x00007fb678429f4b in child_main (child_num_arg=<value optimized out>) at /usr/src/debug/httpd-2.2.15/server/mpm/prefork/prefork.c:662 #20 0x00007fb67842a21a in make_child (s=0x7fb679cd7860, slot=153) at /usr/src/debug/httpd-2.2.15/server/mpm/prefork/prefork.c:758 #21 0x00007fb67842aea4 in perform_idle_server_maintenance (_pconf=<value optimized out>, plog=<value optimized out>, s=<value optimized out>) at /usr/src/debug/httpd-2.2.15/server/mpm/prefork/prefork.c:893 #22 ap_mpm_run (_pconf=<value optimized out>, plog=<value optimized out>, s=<value optimized out>) at /usr/src/debug/httpd-2.2.15/server/mpm/prefork/prefork.c:1097 #23 0x00007fb678402890 in main (argc=1, argv=0x7fff6fecacb8) at /usr/src/debug/httpd-2.2.15/server/main.c:740 PHP.INI Follows: [PHP] engine = On short_open_tag = On asp_tags = Off precision = 14 y2k_compliance = On output_buffering = 4096 zlib.output_compression = Off implicit_flush = Off unserialize_callback_func = serialize_precision = 100 allow_call_time_pass_reference = Off safe_mode = Off safe_mode_gid = Off safe_mode_include_dir = safe_mode_exec_dir = safe_mode_allowed_env_vars = PHP_ safe_mode_protected_env_vars = LD_LIBRARY_PATH disable_functions = disable_classes = expose_php = On max_execution_time = 30 max_input_time = 60 memory_limit = 128M error_reporting = E_ALL & ~E_DEPRECATED display_errors = Off display_startup_errors = Off log_errors = Off log_errors_max_len = 1024 ignore_repeated_errors = Off ignore_repeated_source = Off report_memleaks = On track_errors = Off html_errors = Off variables_order = "GPCS" request_order = "GP" register_globals = Off register_long_arrays = Off register_argc_argv = Off auto_globals_jit = On post_max_size = 8M magic_quotes_gpc = Off magic_quotes_runtime = Off magic_quotes_sybase = Off auto_prepend_file = auto_append_file = default_mimetype = "text/html" doc_root = user_dir = enable_dl = Off file_uploads = On upload_max_filesize = 2M allow_url_fopen = On allow_url_include = Off default_socket_timeout = 60 [Date] [filter] [iconv] [intl] [sqlite] [sqlite3] [Pcre] [Pdo] [Phar] [Syslog] define_syslog_variables = Off [mail function] SMTP = localhost smtp_port = 25 sendmail_path = /usr/sbin/sendmail -t -i mail.add_x_header = On [SQL] sql.safe_mode = Off [ODBC] odbc.allow_persistent = On odbc.check_persistent = On odbc.max_persistent = -1 odbc.max_links = -1 odbc.defaultlrl = 4096 odbc.defaultbinmode = 1 [MySQL] mysql.allow_persistent = On mysql.max_persistent = -1 mysql.max_links = -1 mysql.default_port = mysql.default_socket = mysql.default_host = mysql.default_user = mysql.default_password = mysql.connect_timeout = 60 mysql.trace_mode = Off [MySQLi] mysqli.max_links = -1 mysqli.default_port = 3306 mysqli.default_socket = mysqli.default_host = mysqli.default_user = mysqli.default_pw = mysqli.reconnect = Off [PostgresSQL] pgsql.allow_persistent = On pgsql.auto_reset_persistent = Off pgsql.max_persistent = -1 pgsql.max_links = -1 pgsql.ignore_notice = 0 pgsql.log_notice = 0 [Sybase-CT] sybct.allow_persistent = On sybct.max_persistent = -1 sybct.max_links = -1 sybct.min_server_severity = 10 sybct.min_client_severity = 10 [bcmath] bcmath.scale = 0 [browscap] [Session] session.save_handler = files session.save_path = "/var/lib/php/session" session.use_cookies = 1 session.use_only_cookies = 1 session.name = PHPSESSID session.auto_start = 1 session.cookie_lifetime = 0 session.cookie_path = / session.cookie_domain = session.cookie_httponly = session.serialize_handler = php session.gc_probability = 1 session.gc_divisor = 1000 session.gc_maxlifetime = 1440 session.bug_compat_42 = Off session.bug_compat_warn = Off session.referer_check = session.entropy_length = 0 session.entropy_file = session.cache_limiter = nocache session.cache_expire = 180 session.use_trans_sid = 0 session.hash_function = 0 session.hash_bits_per_character = 5 url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=fakeentry" [MSSQL] mssql.allow_persistent = On mssql.max_persistent = -1 mssql.max_links = -1 mssql.min_error_severity = 10 mssql.min_message_severity = 10 mssql.compatability_mode = Off mssql.secure_connection = Off [Assertion] [COM] [mbstring] [gd] [exif] [Tidy] tidy.clean_output = Off [soap] soap.wsdl_cache_enabled=1 soap.wsdl_cache_dir="/tmp" soap.wsdl_cache_ttl=86400 /etc/php.d/memcached.ini : session.save_path="tcp://memcache1:11211?persistent=1&weight=1&timeout=3&retry_interval=15"

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  • What is considered third party code?

    - by Songo
    Inspired by this question Using third-party libraries - always use a wrapper? I wanted to know what people actually consider as third-party libraries. Example from PHP: If I'm building an application using Zend framework, should I treat Zend framework libraries as third party code? Example from C#: If I'm building a desktop application, should I treat all .Net classes as third party code? Example from Java: Should I treat all libraries in the JDK as third party libraries? Some people say that if a library is stable and won't change often then one doesn't need to wrap it. However I fail to see how one would test a class that depends on a third party code without wrapping it.

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  • Go up one directory in mod_rewrite

    - by Rudolph Gottesheim
    I've got a standard Zend Framework 1 project that looks a bit like this: Project |- public |- .htaccess |- index.php The .htaccess looks like this: RewriteEngine On RewriteBase / RewriteRule ^image/.*$ img.php?file=$1 [NC,L] RewriteCond %{REQUEST_FILENAME} -s [OR] RewriteCond %{REQUEST_FILENAME} -l [OR] RewriteCond %{REQUEST_FILENAME} -d RewriteRule ^.*$ - [NC,L] RewriteRule ^.*$ index.php [NC,L] Now I want to start transitioning the site to Zend Framework 2, which I put in a separate directory in the root, so the whole thing looks like this: Project |- public |- .htaccess |- index.php |- zf2 |- public |- .htaccess |- index.php What would I have to change in my original (ZF1) .htaccess to route all requests to (for example) /zf2/whatever to ZF2's index.php? I've tried RewriteRule ^zf2(/.*)$ ../zf2/public/index.php [NC,L] in the line after RewriteBase /, but that just gives me a 400 Bad Request.

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  • Understanding exceptional cases

    - by Justin
    I've been studying the use of exceptions in various php projects (such as Doctrine and Zend Framework). Exceptions seem to be thrown when unordinary input/state occurs. A perfect example is Doctrine throwing an exception when you try to use a invalid query string. I think the creators of the doctrine api understood that first, you can't query data by using an invalid DQL statement, and a developer should immediately be warned that an error has occurred, rather then letting execution continue with the possibility of an error code going un-checked. I also bet that this simplifies reading the code. I can't think of a situation where you would want to use an invalid DQL statement, except unit testing. Since this is true, it's better to avoid plaguing a bunch of code with null/error checks and use exceptions. I've read in books that exceptions shouldn't be thrown when validating dating user input. I've seen examples where of where the guideline is broken. One example is the Zend framework. If supplying an invalid controller or action name, an exception is thrown. Unlike doctrine, the user has more direct control over this sort of input. I know you can configure an error controller and set up a 404 message or what have you, but I'm curious why they have used an exception in this scenario? I guess you can argue the Zend Framework does not know how to continue processing the quest. One last example Is I wrote a function to return some html based on a given resource type. This resource type is hard-coded and sent when a user interacts with a web site (such as clicking a button to display the form to input data). I don't expect users to be mucking around with the request type. Under normal operating conditions, the resource type should be valid. To clean up some logic, I was going to throw an exception if a particular form wasn't found. This is mainly to find the correct form associated with a resource type so proper validation can occur. Does this sound like a valid use case for an exception? Right now it's pretty trivial, but I do plan to implement a restful consumer and re-using a function to map resources to their validation services would be very useful. I can then catch the exception and based on the consumer, return an error message suitable for the request type...

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  • What are famous windows programming framework in work field?

    - by Moon
    Hi, I am a php programmer. Ever since I started working in php industry, companies I worked with used zend framework, codeigniter, and cake php. So...in windows programming world, what are equivalent to zend framework, codeigniter, and cake php? The reason I am asking this question is because I am about to start windows programming. I am not asking for a certain language. I would like to know many frameworks as possible. p.s: someone please add 'framework' and 'popular' tags for me...

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  • xdebug 2.2.1 installed but not working with cgi

    - by ts01
    I've installed (via pecl) xdebug. It is installed (as phpinfo() output indicates), but it doesn't seems to work with CGI (with CLI it works). I've restarted apache, without result. Any ideas? Some config details (as parsed by http://xdebug.org/wizard.php) Xdebug installed: 2.2.1 Server API: Apache 2.0 Handler Windows: no Zend Server: no PHP Version: 5.3.10-1 Zend API nr: 220090626 PHP API nr: 20090626 Debug Build: no Thread Safe Build: no Configuration File Path: /etc/php5/apache2 Configuration File: /etc/php5/apache2/php.ini Extensions directory: /usr/lib/php5/20090626+lfs

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  • Why is an inverse loop faster than a normal loop (test included)

    - by Saif Bechan
    I have been running some small tests in PHP on loops. I do not know if my method is good. I have found that a inverse loop is faster than a normal loop. I have also found that a while-loop is faster than a for-loop. Setup <?php $counter = 10000000; $w=0;$x=0;$y=0;$z=0; $wstart=0;$xstart=0;$ystart=0;$zstart=0; $wend=0;$xend=0;$yend=0;$zend=0; $wstart = microtime(true); for($w=0; $w<$counter; $w++){ echo ''; } $wend = microtime(true); echo "normal for: " . ($wend - $wstart) . "<br />"; $xstart = microtime(true); for($x=$counter; $x>0; $x--){ echo ''; } $xend = microtime(true); echo "inverse for: " . ($xend - $xstart) . "<br />"; echo "<hr> normal - inverse: " . (($wend - $wstart) - ($xend - $xstart)) . "<hr>"; $ystart = microtime(true); $y=0; while($y<$counter){ echo ''; $y++; } $yend = microtime(true); echo "normal while: " . ($yend - $ystart) . "<br />"; $zstart = microtime(true); $z=$counter; while($z>0){ echo ''; $z--; } $zend = microtime(true); echo "inverse while: " . ($zend - $zstart) . "<br />"; echo "<hr> normal - inverse: " . (($yend - $ystart) - ($zend - $zstart)) . "<hr>"; echo "<hr> inverse for - inverse while: " . (($xend - $xstart) - ($zend - $zstart)) . "<hr>"; ?> Average Results The difference in for-loop normal for: 1.0908501148224 inverse for: 1.0212800502777 normal - inverse: 0.069570064544678 The difference in while-loop normal while: 1.0395669937134 inverse while: 0.99321985244751 normal - inverse: 0.046347141265869 The difference in for-loop and while-loop inverse for - inverse while: 0.0280601978302 Questions My question is can someone explain these differences in results? And is my method of benchmarking been correct?

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  • How do I create statistics to make ‘small’ objects appear ‘large’ to the Optmizer?

    - by Maria Colgan
    I recently spoke with a customer who has a development environment that is a tiny fraction of the size of their production environment. His team has been tasked with identifying problem SQL statements in this development environment before new code is released into production. The problem is the objects in the development environment are so small, the execution plans selected in the development environment rarely reflects what actually happens in production. To ensure the development environment accurately reflects production, in the eyes of the Optimizer, the statistics used in the development environment must be the same as the statistics used in production. This can be achieved by exporting the statistics from production and import them into the development environment. Even though the underlying objects are a fraction of the size of production, the Optimizer will see them as the same size and treat them the same way as it would in production. Below are the necessary steps to achieve this in their environment. I am using the SH sample schema as the application schema who's statistics we want to move from production to development. Step 1. Create a staging table, in the production environment, where the statistics can be stored Step 2. Export the statistics for the application schema, from the data dictionary in production, into the staging table Step 3. Create an Oracle directory on the production system where the export of the staging table will reside and grant the SH user the necessary privileges on it. Step 4. Export the staging table from production using data pump export Step 5. Copy the dump file containing the stating table from production to development Step 6. Create an Oracle directory on the development system where the export of the staging table resides and grant the SH user the necessary privileges on it.  Step 7. Import the staging table into the development environment using data pump import Step 8. Import the statistics from the staging table into the dictionary in the development environment. You can get a copy of the script I used to generate this post here. +Maria Colgan

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  • Hello Operator, My Switch Is Bored

    - by Paul White
    This is a post for T-SQL Tuesday #43 hosted by my good friend Rob Farley. The topic this month is Plan Operators. I haven’t taken part in T-SQL Tuesday before, but I do like to write about execution plans, so this seemed like a good time to start. This post is in two parts. The first part is primarily an excuse to use a pretty bad play on words in the title of this blog post (if you’re too young to know what a telephone operator or a switchboard is, I hate you). The second part of the post looks at an invisible query plan operator (so to speak). 1. My Switch Is Bored Allow me to present the rare and interesting execution plan operator, Switch: Books Online has this to say about Switch: Following that description, I had a go at producing a Fast Forward Cursor plan that used the TOP operator, but had no luck. That may be due to my lack of skill with cursors, I’m not too sure. The only application of Switch in SQL Server 2012 that I am familiar with requires a local partitioned view: CREATE TABLE dbo.T1 (c1 int NOT NULL CHECK (c1 BETWEEN 00 AND 24)); CREATE TABLE dbo.T2 (c1 int NOT NULL CHECK (c1 BETWEEN 25 AND 49)); CREATE TABLE dbo.T3 (c1 int NOT NULL CHECK (c1 BETWEEN 50 AND 74)); CREATE TABLE dbo.T4 (c1 int NOT NULL CHECK (c1 BETWEEN 75 AND 99)); GO CREATE VIEW V1 AS SELECT c1 FROM dbo.T1 UNION ALL SELECT c1 FROM dbo.T2 UNION ALL SELECT c1 FROM dbo.T3 UNION ALL SELECT c1 FROM dbo.T4; Not only that, but it needs an updatable local partitioned view. We’ll need some primary keys to meet that requirement: ALTER TABLE dbo.T1 ADD CONSTRAINT PK_T1 PRIMARY KEY (c1);   ALTER TABLE dbo.T2 ADD CONSTRAINT PK_T2 PRIMARY KEY (c1);   ALTER TABLE dbo.T3 ADD CONSTRAINT PK_T3 PRIMARY KEY (c1);   ALTER TABLE dbo.T4 ADD CONSTRAINT PK_T4 PRIMARY KEY (c1); We also need an INSERT statement that references the view. Even more specifically, to see a Switch operator, we need to perform a single-row insert (multi-row inserts use a different plan shape): INSERT dbo.V1 (c1) VALUES (1); And now…the execution plan: The Constant Scan manufactures a single row with no columns. The Compute Scalar works out which partition of the view the new value should go in. The Assert checks that the computed partition number is not null (if it is, an error is returned). The Nested Loops Join executes exactly once, with the partition id as an outer reference (correlated parameter). The Switch operator checks the value of the parameter and executes the corresponding input only. If the partition id is 0, the uppermost Clustered Index Insert is executed, adding a row to table T1. If the partition id is 1, the next lower Clustered Index Insert is executed, adding a row to table T2…and so on. In case you were wondering, here’s a query and execution plan for a multi-row insert to the view: INSERT dbo.V1 (c1) VALUES (1), (2); Yuck! An Eager Table Spool and four Filters! I prefer the Switch plan. My guess is that almost all the old strategies that used a Switch operator have been replaced over time, using things like a regular Concatenation Union All combined with Start-Up Filters on its inputs. Other new (relative to the Switch operator) features like table partitioning have specific execution plan support that doesn’t need the Switch operator either. This feels like a bit of a shame, but perhaps it is just nostalgia on my part, it’s hard to know. Please do let me know if you encounter a query that can still use the Switch operator in 2012 – it must be very bored if this is the only possible modern usage! 2. Invisible Plan Operators The second part of this post uses an example based on a question Dave Ballantyne asked using the SQL Sentry Plan Explorer plan upload facility. If you haven’t tried that yet, make sure you’re on the latest version of the (free) Plan Explorer software, and then click the Post to SQLPerformance.com button. That will create a site question with the query plan attached (which can be anonymized if the plan contains sensitive information). Aaron Bertrand and I keep a close eye on questions there, so if you have ever wanted to ask a query plan question of either of us, that’s a good way to do it. The problem The issue I want to talk about revolves around a query issued against a calendar table. The script below creates a simplified version and adds 100 years of per-day information to it: USE tempdb; GO CREATE TABLE dbo.Calendar ( dt date NOT NULL, isWeekday bit NOT NULL, theYear smallint NOT NULL,   CONSTRAINT PK__dbo_Calendar_dt PRIMARY KEY CLUSTERED (dt) ); GO -- Monday is the first day of the week for me SET DATEFIRST 1;   -- Add 100 years of data INSERT dbo.Calendar WITH (TABLOCKX) (dt, isWeekday, theYear) SELECT CA.dt, isWeekday = CASE WHEN DATEPART(WEEKDAY, CA.dt) IN (6, 7) THEN 0 ELSE 1 END, theYear = YEAR(CA.dt) FROM Sandpit.dbo.Numbers AS N CROSS APPLY ( VALUES (DATEADD(DAY, N.n - 1, CONVERT(date, '01 Jan 2000', 113))) ) AS CA (dt) WHERE N.n BETWEEN 1 AND 36525; The following query counts the number of weekend days in 2013: SELECT Days = COUNT_BIG(*) FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; It returns the correct result (104) using the following execution plan: The query optimizer has managed to estimate the number of rows returned from the table exactly, based purely on the default statistics created separately on the two columns referenced in the query’s WHERE clause. (Well, almost exactly, the unrounded estimate is 104.289 rows.) There is already an invisible operator in this query plan – a Filter operator used to apply the WHERE clause predicates. We can see it by re-running the query with the enormously useful (but undocumented) trace flag 9130 enabled: Now we can see the full picture. The whole table is scanned, returning all 36,525 rows, before the Filter narrows that down to just the 104 we want. Without the trace flag, the Filter is incorporated in the Clustered Index Scan as a residual predicate. It is a little bit more efficient than using a separate operator, but residual predicates are still something you will want to avoid where possible. The estimates are still spot on though: Anyway, looking to improve the performance of this query, Dave added the following filtered index to the Calendar table: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear) WHERE isWeekday = 0; The original query now produces a much more efficient plan: Unfortunately, the estimated number of rows produced by the seek is now wrong (365 instead of 104): What’s going on? The estimate was spot on before we added the index! Explanation You might want to grab a coffee for this bit. Using another trace flag or two (8606 and 8612) we can see that the cardinality estimates were exactly right initially: The highlighted information shows the initial cardinality estimates for the base table (36,525 rows), the result of applying the two relational selects in our WHERE clause (104 rows), and after performing the COUNT_BIG(*) group by aggregate (1 row). All of these are correct, but that was before cost-based optimization got involved :) Cost-based optimization When cost-based optimization starts up, the logical tree above is copied into a structure (the ‘memo’) that has one group per logical operation (roughly speaking). The logical read of the base table (LogOp_Get) ends up in group 7; the two predicates (LogOp_Select) end up in group 8 (with the details of the selections in subgroups 0-6). These two groups still have the correct cardinalities as trace flag 8608 output (initial memo contents) shows: During cost-based optimization, a rule called SelToIdxStrategy runs on group 8. It’s job is to match logical selections to indexable expressions (SARGs). It successfully matches the selections (theYear = 2013, is Weekday = 0) to the filtered index, and writes a new alternative into the memo structure. The new alternative is entered into group 8 as option 1 (option 0 was the original LogOp_Select): The new alternative is to do nothing (PhyOp_NOP = no operation), but to instead follow the new logical instructions listed below the NOP. The LogOp_GetIdx (full read of an index) goes into group 21, and the LogOp_SelectIdx (selection on an index) is placed in group 22, operating on the result of group 21. The definition of the comparison ‘the Year = 2013’ (ScaOp_Comp downwards) was already present in the memo starting at group 2, so no new memo groups are created for that. New Cardinality Estimates The new memo groups require two new cardinality estimates to be derived. First, LogOp_Idx (full read of the index) gets a predicted cardinality of 10,436. This number comes from the filtered index statistics: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH STAT_HEADER; The second new cardinality derivation is for the LogOp_SelectIdx applying the predicate (theYear = 2013). To get a number for this, the cardinality estimator uses statistics for the column ‘theYear’, producing an estimate of 365 rows (there are 365 days in 2013!): DBCC SHOW_STATISTICS (Calendar, theYear) WITH HISTOGRAM; This is where the mistake happens. Cardinality estimation should have used the filtered index statistics here, to get an estimate of 104 rows: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH HISTOGRAM; Unfortunately, the logic has lost sight of the link between the read of the filtered index (LogOp_GetIdx) in group 22, and the selection on that index (LogOp_SelectIdx) that it is deriving a cardinality estimate for, in group 21. The correct cardinality estimate (104 rows) is still present in the memo, attached to group 8, but that group now has a PhyOp_NOP implementation. Skipping over the rest of cost-based optimization (in a belated attempt at brevity) we can see the optimizer’s final output using trace flag 8607: This output shows the (incorrect, but understandable) 365 row estimate for the index range operation, and the correct 104 estimate still attached to its PhyOp_NOP. This tree still has to go through a few post-optimizer rewrites and ‘copy out’ from the memo structure into a tree suitable for the execution engine. One step in this process removes PhyOp_NOP, discarding its 104-row cardinality estimate as it does so. To finish this section on a more positive note, consider what happens if we add an OVER clause to the query aggregate. This isn’t intended to be a ‘fix’ of any sort, I just want to show you that the 104 estimate can survive and be used if later cardinality estimation needs it: SELECT Days = COUNT_BIG(*) OVER () FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; The estimated execution plan is: Note the 365 estimate at the Index Seek, but the 104 lives again at the Segment! We can imagine the lost predicate ‘isWeekday = 0’ as sitting between the seek and the segment in an invisible Filter operator that drops the estimate from 365 to 104. Even though the NOP group is removed after optimization (so we don’t see it in the execution plan) bear in mind that all cost-based choices were made with the 104-row memo group present, so although things look a bit odd, it shouldn’t affect the optimizer’s plan selection. I should also mention that we can work around the estimation issue by including the index’s filtering columns in the index key: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear, isWeekday) WHERE isWeekday = 0 WITH (DROP_EXISTING = ON); There are some downsides to doing this, including that changes to the isWeekday column may now require Halloween Protection, but that is unlikely to be a big problem for a static calendar table ;)  With the updated index in place, the original query produces an execution plan with the correct cardinality estimation showing at the Index Seek: That’s all for today, remember to let me know about any Switch plans you come across on a modern instance of SQL Server! Finally, here are some other posts of mine that cover other plan operators: Segment and Sequence Project Common Subexpression Spools Why Plan Operators Run Backwards Row Goals and the Top Operator Hash Match Flow Distinct Top N Sort Index Spools and Page Splits Singleton and Range Seeks Bitmaps Hash Join Performance Compute Scalar © 2013 Paul White – All Rights Reserved Twitter: @SQL_Kiwi

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  • Unused Indexes Gotcha

    - by DavidWimbush
    I'm currently looking into dropping unused indexes to reduce unnecessary overhead and I came across a very good point in the excellent SQL Server MVP Deep Dives book that I haven't seen highlighted anywhere else. I was thinking it was simply a case of dropping indexes that didn't show as being used in DMV sys.dm_db_index_usage_stats (assuming a solid representative workload had been run since the last service start). But Rob Farley points out that the DMV only shows indexes whose pages have been read or updated. An index that isn't listed in the DMV might still be useful by providing metadata to the Query Optimizer and thus streamlining query plans. For example, if you have a query like this: select  au.author_name         , count(*) as books from    books b         inner join authors au on au.author_id = b.author_id group by au.author_name If you have a unique index on authors.author_name the Query Optimizer will realise that each author_id will have a different author_name so it can produce a plan that just counts the books by author_id and then adds the author name to each row in that small table. If you delete that index the query will have to join all the books with their authors and then apply the GROUP BY - a much more expensive query. So be cautious about dropping apparently unused unique indexes.

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  • Column order can matter

    - by Dave Ballantyne
    Ordinarily, column order of a SQL statement does not matter. Select a,b,c from table will produce the same execution plan as   Select c,b,a from table However, sometimes it can make a difference.   Consider this statement (maxdop is used to make a simpler plan and has no impact to the main point):   select SalesOrderID, CustomerID, OrderDate, ROW_NUMBER() over (Partition By CustomerId order by OrderDate asc) as RownAsc, ROW_NUMBER() over (Partition By CustomerId order by OrderDate Desc) as RownDesc from sales.SalesOrderHeader order by CustomerID,OrderDateoption(maxdop 1) If you look at the execution plan, you will see similar to this That is three sorts.  One for RownAsc,  one for RownDesc and the final one for the ‘Order by’ clause.  Sorting is an expensive operation and one that should be avoided if possible.  So with this in mind, it may come as some surprise that the optimizer does not re-order operations to group them together when the incoming data is in a similar (if not exactly the same) sorted sequence.  A simple change to swap the RownAsc and RownDesc columns to produce this statement : select SalesOrderID, CustomerID, OrderDate, ROW_NUMBER() over (Partition By CustomerId order by OrderDate Desc) as RownDesc , ROW_NUMBER() over (Partition By CustomerId order by OrderDate asc) as RownAsc from Sales.SalesOrderHeader order by CustomerID,OrderDateoption(maxdop 1) Will result a different and more efficient query plan with one less sort. The optimizer, although unable to automatically re-order operations, HAS taken advantage of the data ordering if it is as required.  This is well worth taking advantage of if you have different sorting requirements in one statement. Try grouping the functions that require the same order together and save yourself a few extra sorts.

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  • "Unable to initialize module" fileinfo php-pecl-Fileinfo.x86_64

    - by Myers Network
    I have a brand new server server that I am trying to get setup up. This is a 64 bit machine that I can not install "fileinfo" or "memcache". I have uninstalled these and reinstalled them using yum and pecl with no luck. Yum install fine "no error" but then get error when running php. pecl from what I can tell is only installing 32bit. Does not put anything in the lib64 directory. Here is my output from php -v: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP 5.2.14 (cli) (built: Aug 12 2010 16:03:48) Copyright (c) 1997-2010 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies Here is some other system info incase you need it uname: Linux server.actham.us 2.6.18-194.26.1.el5 #1 SMP Tue Nov 9 12:54:20 EST 2010 x86_64 x86_64 x86_64 GNU/Linux php -m: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 [PHP Modules] bz2 calendar ctype curl date dbase dom exif filter ftp gd gettext gmp hash iconv imap json ldap libxml mbstring mcrypt mysql mysqli openssl pcntl pcre PDO pdo_mysql pdo_sqlite readline Reflection session shmop SimpleXML sockets SPL standard tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl zip zlib [Zend Modules] Any help would be greatly appreciated, thanks....

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  • "Unable to initialize module" fileinfo php-pecl-Fileinfo.x86_64

    - by Myers Network
    I have a brand new server server that I am trying to get setup up. This is a 64 bit machine that I can not install "fileinfo" or "memcache". I have uninstalled these and reinstalled them using yum and pecl with no luck. Yum install fine "no error" but then get error when running php. pecl from what I can tell is only installing 32bit. Does not put anything in the lib64 directory. Here is my output from php -v: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP 5.2.14 (cli) (built: Aug 12 2010 16:03:48) Copyright (c) 1997-2010 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies Here is some other system info incase you need it uname: Linux server.actham.us 2.6.18-194.26.1.el5 #1 SMP Tue Nov 9 12:54:20 EST 2010 x86_64 x86_64 x86_64 GNU/Linux php -m: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 [PHP Modules] bz2 calendar ctype curl date dbase dom exif filter ftp gd gettext gmp hash iconv imap json ldap libxml mbstring mcrypt mysql mysqli openssl pcntl pcre PDO pdo_mysql pdo_sqlite readline Reflection session shmop SimpleXML sockets SPL standard tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl zip zlib [Zend Modules] Any help would be greatly appreciated, thanks....

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  • Creating an Apache Virtual Directory, but updating Active Directory DNS

    - by SnoConeGod
    Hello all, I'm just getting started with using the Zend Framework and am following a recommended procedure where I am supposed to create an Apache Virtual Directory for the public-facing portion of a new Zend project. I don't THINK I had any issues creating the Virtual Directory, but my knowledge of the required DNS changes is rather lacking. The dev server I'm using is on a Microsoft Windows Active Directory domain, so I've added A records for both the server name and the subdomain. Still, trying to browse to the site from a Windows 7 PC isn't working properly. What am I missing? What's the proper set of steps for getting an Apache-served subdomain to appear properly in a peer computer's web browser? Details below: server: Debian command-line only, freshly installed today with Zend Server CE LAMP stack server name: ZENDEV subdomain: SQUARE.ZENDEV AD Domain functional level: 2008 mixed (run by a mishmash of 03 and 08 servers) attempting to visit the sites: http://square.zendev and http://square.zendev.domain.local (name of domain redacted, but using the local (not com) suffix) Apache Virtual Directory added to httpd.conf: NameVirtualHost *:80 <VirtualHost *:80> DocumentRoot "/var/www/square/public" ServerName square.localhost </VirtualHost> Is this only a problem with DNS? Or with DNS and my Virtual Directory? Thanks! John

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  • Installing ionCube on Windows 2008 64bit

    - by JoJo
    I've been trying to install ionCube onto my server but have not been having a lot of luck! My server is: Windows 2008 64bit PHP 5.3.14 Thread Safe disabled running as FastCGI In my PHP.ini I have : zend_extension="C:\Program Files (x86)\PHP\ext\ioncube_loader_win_5.2.dll" The path is correct. The DLL is from the x86 NONTS VC9 version of ionCube and PHP is using the MSVC9 (Visual C++ 2008) compiler though I have also tried using the x86 NONTS VC6 version of ionCube. I'm not getting any error but I'm also not getting ionCube when using phpinfo(): This program makes use of the Zend Scripting Language Engine: Zend Engine v2.3.0, Copyright (c) 1998-2012 Zend Technologies Apart from the mail application pools I have also set all the applications in the application pool in IIS7 to use 32bit mode. I don't know if FastCGI is running under 64 or 32 bit mode nor how to switch it or whether it would make a difference? I know it can be a problem installing ionCube onto 64bit Windows but I have also come across threads whereby other people have also [somehow] managed to get it working but even though I seem to be doing the same as them I still can't get it working.

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  • Debugging php-cli scripts with xdebug and netbeans?

    - by wurdalack
    I have managed to initiate php-cli script debug session from the IDE itself, but I need to start the debugging session from the shell / command line. These are rather complex maintenance PHP scripts which take a lot of input parameters, so entering arguments from within Netbeans is a bit cumbersome. I have done it before with Zend studio http://kb.zend.com/index.php?View=entry&EntryID=130 but now I need to get it working with Netbeans. Thanks in advance.

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  • What is the best php encoder software ?

    - by question_about_the_problem
    What is the best php encoder software? http://www.freedownloadmanager.org/downloads/php_encoder_software/ http://forums.digitalpoint.com/showthread.php?t=596680 or another. Everybody say Zend Guard. But you can decode/decript zend's files at the page http://www.showmycode.com/ I think, SourceGuardian is good. But I'm not so sure.

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