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Update FAQ.
This commit is contained in:
Bruce Momjian
101
doc/FAQ
101
doc/FAQ
@ -90,10 +90,10 @@
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4.14) In a query, how do I detect if a field is NULL?
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4.15) What is the difference between the various character types?
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4.16.1) How do I create a serial/auto-incrementing field?
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4.16.2) How do I get the value of a serial insert?
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4.16.2) How do I get the value of a SERIAL insert?
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4.16.3) Don't currval() and nextval() lead to a race condition with
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other concurrent backend processes?
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4.17) What is an oid? What is a tid?
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other users?
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4.17) What is an OID? What is a TID?
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4.18) What is the meaning of some of the terms used in PostgreSQL?
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4.19) Why do I get the error "FATAL: palloc failure: memory
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exhausted?"
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@ -108,13 +108,13 @@
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5.1) I wrote a user-defined function. When I run it in psql, why does
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it dump core?
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5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0
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not in alloc set! mean?
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5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0
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not in alloc set!" mean?
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5.3) How can I contribute some nifty new types and functions to
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PostgreSQL?
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5.4) How do I write a C function to return a tuple?
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5.5) I have changed a source file. Why does the recompile does not see
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the change?
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5.5) I have changed a source file. Why does the recompile not see the
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change?
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_________________________________________________________________
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General Questions
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@ -219,8 +219,8 @@
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The main mailing list is: pgsql-general@PostgreSQL.org. It is
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available for discussion of matters pertaining to PostgreSQL. To
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subscribe, send a mail with the lines in the body (not the subject
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line)
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subscribe, send mail with the following lines in the body (not the
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subject line)
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subscribe
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end
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@ -280,8 +280,8 @@
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1.9) How do I find out about known bugs or missing features?
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PostgreSQL supports an extended subset of SQL-92. See our TODO for a
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list of known bugs, missing features, and future plans.
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PostgreSQL supports an extended subset of SQL-92. See our TODO list
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for known bugs, missing features, and future plans.
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1.10) How can I learn SQL?
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@ -303,16 +303,16 @@
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1.12) How do I join the development team?
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First, download the latest sources and read the PostgreSQL Developers
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First, download the latest source and read the PostgreSQL Developers
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documentation on our web site, or in the distribution. Second,
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subscribe to the pgsql-hackers and pgsql-patches mailing lists. Third,
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submit high-quality patches to pgsql-patches.
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There are about a dozen people who have commit privileges to the
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PostgreSQL CVS archive. They each have submitted so many high-quality
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patches that it was a pain for the existing committers to keep up, and
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we had confidence that patches they committed were likely to be of
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high quality.
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patches that it was impossible for the existing committers to keep up,
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and we had confidence that patches they committed were of high
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quality.
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1.13) How do I submit a bug report?
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@ -333,7 +333,7 @@
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some features they don't have, like user-defined types,
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inheritance, rules, and multi-version concurrency control to
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reduce lock contention. We don't have outer joins, but are
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working on them for our next release.
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working on them.
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Performance
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PostgreSQL runs in two modes. Normal fsync mode flushes every
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@ -442,7 +442,7 @@
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* Python(PyGreSQL)
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* TCL(libpgtcl)
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* C Easy API(libpgeasy)
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* Embedded HTML(PHP from http://www.php.net)
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* Embedded HTML (PHP from http://www.php.net)
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_________________________________________________________________
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Administrative Questions
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@ -474,9 +474,9 @@
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You either do not have shared memory configured properly in your
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kernel or you need to enlarge the shared memory available in the
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kernel. The exact amount you need depends on your architecture and how
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many buffers and backend processes you configure postmaster to run
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with. For most systems, with default numbers of buffers and processes,
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you need a minimum of ~1MB.
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many buffers and backend processes you configure for the postmaster.
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For most systems, with default numbers of buffers and processes, you
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need a minimum of ~1MB.
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3.5) When I try to start the postmaster, I get IpcSemaphoreCreate errors.
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Why?
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@ -511,7 +511,7 @@
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You should not create database users with user id 0 (root). They will
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be unable to access the database. This is a security precaution
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because of the ability of any user to dynamically link object modules
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because of the ability of users to dynamically link object modules
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into the database engine.
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3.9) All my servers crash under concurrent table access. Why?
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@ -533,9 +533,9 @@
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reduces the transaction overhead. Also consider dropping and
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recreating indices when making large data changes.
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There are several tuning things that can be done. You can disable
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fsync() by starting the postmaster with a -o -F option. This will
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prevent fsync()'s from flushing to disk after every transaction.
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There are several tuning options. You can disable fsync() by starting
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the postmaster with a -o -F option. This will prevent fsync()'s from
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flushing to disk after every transaction.
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You can also use the postmaster -B option to increase the number of
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shared memory buffers used by the backend processes. If you make this
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@ -548,7 +548,7 @@
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value is measured in kilobytes, and the default is 512 (ie, 512K).
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You can also use the CLUSTER command to group data in tables to match
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an index. See the cluster(l) manual page for more details.
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an index. See the CLUSTER manual page for more details.
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3.11) What debugging features are available?
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@ -629,8 +629,8 @@
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They are temporary files generated by the query executor. For example,
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if a sort needs to be done to satisfy an ORDER BY, and the sort
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requires more space than the backend's -S parameter allows, then temp
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files are created to hold the extra data.
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requires more space than the backend's -S parameter allows, then
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temporary files are created to hold the extra data.
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The temp files should be deleted automatically, but might not if a
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backend crashes during a sort. If you have no backends running at the
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@ -695,7 +695,7 @@ Maximum number of indexes on a table? unlimited
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BLCKSZ. To use attributes larger than 8K, you can also use the large
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object interface.
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Row length limit will be removed in 7.1.
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The row length limit will be removed in 7.1.
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4.7)How much database disk space is required to store data from a typical
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text file?
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@ -847,13 +847,13 @@ BYTEA bytea variable-length array of bytes
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CREATE UNIQUE INDEX person_id_key ON person ( id );
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See the create_sequence manual page for more information about
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sequences. You can also use each row's oid field as a unique value.
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sequences. You can also use each row's OID field as a unique value.
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However, if you need to dump and reload the database, you need to use
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pg_dump's -o option or COPY WITH OIDS option to preserve the oids.
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pg_dump's -o option or COPY WITH OIDS option to preserve the OIDs.
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Numbering Rows.
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4.16.2) How do I get the back the generated SERIAL value after an insert?
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4.16.2) How do I get the value of a SERIAL insert?
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One approach is to to retrieve the next SERIAL value from the sequence
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object with the nextval() function before inserting and then insert it
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@ -873,35 +873,35 @@ BYTEA bytea variable-length array of bytes
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INSERT INTO person (name) VALUES ('Blaise Pascal');
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$newID = currval('person_id_seq');
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Finally, you could use the oid returned from the INSERT statement to
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Finally, you could use the OID returned from the INSERT statement to
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lookup the default value, though this is probably the least portable
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approach. In perl, using DBI with Edmund Mergl's DBD::Pg module, the
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oid value is made available via $sth->{pg_oid_status} after
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$sth->execute().
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4.16.3) Don't currval() and nextval() lead to a race condition with other
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concurrent backend processes?
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users?
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No. This is handled by the backends.
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4.17) What is an oid? What is a tid?
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4.17) What is an OID? What is a TID?
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OIDs are PostgreSQL's answer to unique row ids. Every row that is
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created in PostgreSQL gets a unique oid. All oids generated during
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created in PostgreSQL gets a unique OID. All OIDs generated during
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initdb are less than 16384 (from backend/access/transam.h). All
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user-created oids are equal or greater that this. By default, all
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these oids are unique not only within a table, or database, but unique
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user-created OIDs are equal or greater that this. By default, all
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these OIDs are unique not only within a table, or database, but unique
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within the entire PostgreSQL installation.
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PostgreSQL uses oids in its internal system tables to link rows
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between tables. These oids can be used to identify specific user rows
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and used in joins. It is recommended you use column type oid to store
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oid values. You can create an index on the oid field for faster
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PostgreSQL uses OIDs in its internal system tables to link rows
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between tables. These OIDs can be used to identify specific user rows
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and used in joins. It is recommended you use column type OID to store
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OID values. You can create an index on the OID field for faster
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access.
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Oids are assigned to all new rows from a central area that is used by
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all databases. If you want to change the oid to something else, or if
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you want to make a copy of the table, with the original oid's, there
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all databases. If you want to change the OID to something else, or if
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you want to make a copy of the table, with the original OID's, there
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is no reason you can't do it:
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CREATE TABLE new_table(old_oid oid, mycol int);
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SELECT old_oid, mycol INTO new FROM old;
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@ -909,7 +909,7 @@ BYTEA bytea variable-length array of bytes
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DELETE FROM new;
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COPY new WITH OIDS FROM '/tmp/pgtable';
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Tids are used to identify specific physical rows with block and offset
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TIDs are used to identify specific physical rows with block and offset
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values. Tids change after rows are modified or reloaded. They are used
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by index entries to point to physical rows.
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@ -923,7 +923,7 @@ BYTEA bytea variable-length array of bytes
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* retrieve, select
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* replace, update
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* append, insert
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* oid, serial value
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* OID, serial value
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* portal, cursor
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* range variable, table name, table alias
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@ -969,7 +969,7 @@ BYTEA bytea variable-length array of bytes
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Currently, we join subqueries to outer queries by sequential scanning
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the result of the subquery for each row of the outer query. A
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workaround is to replace IN with EXISTS. For example, change:
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workaround is to replace IN with EXISTS:
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SELECT *
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FROM tab
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WHERE col1 IN (SELECT col2 FROM TAB2)
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@ -1005,8 +1005,8 @@ BYTEA bytea variable-length array of bytes
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The problem could be a number of things. Try testing your user-defined
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function in a stand alone test program first.
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5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
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alloc set! mean?
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5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
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alloc set!" mean?
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You are pfree'ing something that was not palloc'ed. Beware of mixing
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malloc/free and palloc/pfree.
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@ -1021,9 +1021,8 @@ BYTEA bytea variable-length array of bytes
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This requires wizardry so extreme that the authors have never tried
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it, though in principle it can be done.
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5.5) I have changed a source file. Why does the recompile does not see the
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5.5) I have changed a source file. Why does the recompile not see the
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change?
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The Makefiles do not have the proper dependencies for include files.
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You have to do a make clean and then another make. You have to do a
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make clean and then another make.
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You have to do a make clean and then another make.
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Reference in New Issue
Block a user