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Diffstat (limited to 'doc/FAQ')
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1 files changed, 35 insertions, 28 deletions
@@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Sat Oct 24 00:12:23 EDT 1998 + Last updated: Sat Dec 12 22:56:56 EST 1998 Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us) @@ -68,8 +68,7 @@ cursors? 3.5) What is an R-tree index and what is it used for? 3.6) What is the maximum size for a tuple? - 3.7) I defined indices but my queries don't seem to make use of them. - Why? + 3.7) My queries are slow or don't make use of the indexes. Why? 3.8) How do I do regular expression searches? case-insensitive regexp searching? 3.9) I experienced a server crash during a vacuum. How do I remove the @@ -275,7 +274,7 @@ Section 1: General Questions pg_upgrade utility. Those upgrading from earlier releases require a dump and restore. - Those ugrading from versions earlier than 1.09 must upgrade to 1.09 + Those upgrading from versions earlier than 1.09 must upgrade to 1.09 first without a dump/reload, then dump the data from 1.09, and then load it into 6.4. @@ -306,14 +305,14 @@ Section 1: General Questions PHP is great for simple stuff, but for more complex stuff, some still use the perl interface and CGI.pm. - An WWW gatway based on WDB using perl can be downloaded from + An WWW gateway based on WDB using perl can be downloaded from http://www.eol.ists.ca/~dunlop/wdb-p95 1.13) Does PostgreSQL have a graphical user interface? A report generator? A embedded query language interface? We have a nice graphical user interface called pgaccess, which is - shipped as part of the distribtion. Pgaccess also has a report + shipped as part of the distribution. Pgaccess also has a report generator. The web page is http://www.flex.ro/pgaccess We also include ecpg, @@ -433,7 +432,7 @@ Section 2: Installation Questions You can also use the postgres -S option to increase the maximum amount of memory used by each backend process for temporary sorts. Each - buffer is 1K and the defualt is 512 buffers. + buffer is 1K and the default is 512 buffers. You can also use the cluster command to group data in base tables to match an index. See the cluster(l) manual page for more details. @@ -471,7 +470,7 @@ Section 2: Installation Questions operating system can attach to a running backend directly to diagnose problems. - The postgres program has a -s, -A, -t options that can be very usefull + The postgres program has a -s, -A, -t options that can be very useful for debugging and performance measurements. You can also compile with profiling to see what functions are taking @@ -483,7 +482,7 @@ Section 2: Installation Questions Edit include/storage/sinvaladt.h, and change the value of MaxBackendId. In the future, we plan to make this a configurable - prameter. + parameter. 2.14) What non-unix ports are available? @@ -492,12 +491,16 @@ Section 2: Installation Questions the client is running on MS Windows, and communicates via TCP/IP to a server running on one of our supported Unix platforms. - A file win32.mak is included in the distributiion for making a Win32 + A file win32.mak is included in the distribution for making a Win32 libpq library and psql. - Someone is attempting to port our PostgreSQL database server to - Windows NT using the Cygnus Unix/NT porting library. He has gotten it - compiled, but initdb is currently failing. + The database server is now working on Windows NT using the Cygnus + Unix/NT porting library. The only feature missing is dynamic loading + of user-defined functions/types. See + http://www.askesis.nl/AskesisPostgresIndex.html for more information. + + There is another port using U/Win at + http://surya.wipro.com/uwin/ported.html. _________________________________________________________________ Section 3: PostgreSQL Features @@ -569,22 +572,28 @@ Section 3: PostgreSQL Features Tuples do not cross 8k boundaries so a 5k tuple will require 8k of storage. - 3.7) I defined indices but my queries don't seem to make use of them. Why? + 3.7) My queries are slow or don't make use of the indexes. Why? PostgreSQL does not automatically maintain statistics. One has to make an explicit vacuum call to update the statistics. After statistics are updated, the optimizer knows how many rows in the table, and can better decide if it should use indices. Note that the optimizer does - not use indices in cases when the table is small because a sequentail - scan would be faster. For column-specific optimization statistics, use - vacuum analyze. + not use indices in cases when the table is small because a sequential + scan would be faster. + + For column-specific optimization statistics, use vacuum analyze. + Vacuum analyze is important for complex multi-join queries, so the + optimizer can estimate the number of rows returned from each table, + and choose the proper join order. The backend does not keep track of + column statistics on its own, and vacuum analyze must be run to + collect them periodically. Indexes are not used for order by operations. - When using wildcard operators like LIKE or ~, indices can only be used - if the beginning of the search is anchored to the start of the string. - So, to use indices, LIKE searches can should not begin with %, and - ~(regular expression searches) should start with ^. + When using wild-card operators like LIKE or ~, indices can only be + used if the beginning of the search is anchored to the start of the + string. So, to use indices, LIKE searches can should not begin with %, + and ~(regular expression searches) should start with ^. 3.8) How do I do regular expression searches? case-insensitive regexp searching? @@ -681,9 +690,9 @@ BYTEA bytea variable-length array of bytes CREATE TABLE new_table (mycol int); INSERT INTO new_table SELECT oid, mycol FROM old_table; - Tids are used to indentify specific physical rows with block and - offset values. Tids change after rows are modified or reloaded. They - are used by index entries to point to physical rows. + Tids are used to identify specific physical rows with block and offset + values. Tids change after rows are modified or reloaded. They are used + by index entries to point to physical rows. 3.18) What is the meaning of some of the terms used in PostgreSQL? @@ -794,10 +803,8 @@ Section 4: Extending PostgreSQL 4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set! - You are pfree'ing something that was not palloc'ed. When writing - user-defined functions, do not include the file "libpq-fe.h". Doing so - will cause your palloc to be a malloc instead of a free. Then, when - the backend pfrees the storage, you get the notice message. + You are pfree'ing something that was not palloc'ed. Beware of mixing + malloc/free and palloc/pfree. 4.3) I've written some nifty new types and functions for PostgreSQL. |