database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-28 23:42:10 +03:00
Code Activity

Update FAQ.

Browse Source
This commit is contained in:
Bruce Momjian
2000-10-05 05:14:58 +00:00
parent 1ba857513d
commit bc11dd61d3
2 changed files with 58 additions and 48 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
doc/FAQ
View File

@ -691,7 +691,7 @@ Maximum number of indexes on a table? unlimited
4.7)How much database disk space is required to store data from a typical
text file?
A PostgreSQL database may need six and a half times the disk space
A PostgreSQL database may need six-and-a-half times the disk space
required to store the data in a flat file.
Consider a file of 300,000 lines with two integers on each line. The
@ -738,7 +738,7 @@ Maximum number of indexes on a table? unlimited
faster.
For column-specific optimization statistics, use VACUUM ANALYZE.
VACUUM ANALYZE is important for complex multi-join queries, so the
VACUUM ANALYZE is important for complex multijoin 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, so VACUUM ANALYZE must be run to collect
@ -763,34 +763,34 @@ Maximum number of indexes on a table? unlimited
handle range searches. A B-tree index only handles range searches in a
single dimension. R-tree's can handle multi-dimensional data. For
example, if an R-tree index can be built on an attribute of type
point, the system can more efficient answer queries like select all
points within a bounding rectangle.
point, the system can more efficiently answer queries such as "select
all points within a bounding rectangle."
The canonical paper that describes the original R-Tree design is:
The canonical paper that describes the original R-tree design is:
Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial
Guttman, A. "R-trees: A Dynamic Index Structure for Spatial
Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data,
45-57.
You can also find this paper in Stonebraker's "Readings in Database
Systems"
Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
Built-in R-trees can handle polygons and boxes. In theory, R-trees can
be extended to handle higher number of dimensions. In practice,
extending R-trees require a bit of work and we don't currently have
extending R-trees requires a bit of work and we don't currently have
any documentation on how to do it.
4.12) What is Genetic Query Optimization?
The GEQO module speeds query optimization when joining many tables by
means of a Genetic Algorithm (GA). It allows the handling of large
join queries through non-exhaustive search.
join queries through nonexhaustive search.
4.13) How do I do regular expression searches and case-insensitive regular
expression searches?
The ~ operator does regular-expression matching, and ~* does
case-insensitive regular-expression matching. There is no
The ~ operator does regular expression matching, and ~* does
case-insensitive regular expression matching. There is no
case-insensitive variant of the LIKE operator, but you can get the
effect of case-insensitive LIKE with this:
WHERE lower(textfield) LIKE lower(pattern)
@ -812,7 +812,7 @@ BYTEA bytea variable-length array of bytes
You will see the internal name when examining system catalogs and in
some error messages.
The last four types above are "varlena" types (i.e. the first four
The last four types above are "varlena" types (i.e., the first four
bytes are the length, followed by the data). char(#) allocates the
maximum number of bytes no matter how much data is stored in the
field. text, varchar(#), and bytea all have variable length on the
@ -855,17 +855,17 @@ BYTEA bytea variable-length array of bytes
You would then also have the new value stored in $newSerialID for use
in other queries (e.g., as a foreign key to the person table). Note
that the name of the automatically-created SEQUENCE object will be
that the name of the automatically created SEQUENCE object will be
named <table>_<serialcolumn>_seq, where table and serialcolumn are the
names of your table and your SERIAL column, respectively.
Alternatively, you could retrieve the just-assigned SERIAL value with
the currval() function after it was inserted by default, e.g.,
Alternatively, you could retrieve the assigned SERIAL value with the
currval() function after it was inserted by default, e.g.,
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
Finally, you could use the OID returned from the INSERT statement to
lookup the default value, though this is probably the least portable
look up the default value, though this is probably the least portable
approach. In Perl, using DBI with Edmund Mergl's DBD::Pg module, the
oid value is made available via $sth->{pg_oid_status} after
$sth->execute().
@ -880,8 +880,8 @@ BYTEA bytea variable-length array of bytes
OIDs are PostgreSQL's answer to unique row ids. Every row that is
created in PostgreSQL gets a unique OID. All OIDs generated during
initdb are less than 16384 (from backend/access/transam.h). All
user-created OIDs are equal or greater that this. By default, all
these OIDs are unique not only within a table, or database, but unique
user-created OIDs are equal to or greater than this. By default, all
these OIDs are unique not only within a table or database, but unique
within the entire PostgreSQL installation.
PostgreSQL uses OIDs in its internal system tables to link rows
@ -965,8 +965,8 @@ BYTEA bytea variable-length array of bytes
4.23) Why are my subqueries using IN so slow?
Currently, we join subqueries to outer queries by sequential scanning
the result of the subquery for each row of the outer query. A
Currently, we join subqueries to outer queries by sequentially
scanning the result of the subquery for each row of the outer query. A
workaround is to replace IN with EXISTS:
SELECT *
FROM tab
@ -1001,7 +1001,7 @@ BYTEA bytea variable-length array of bytes
dump core?
The problem could be a number of things. Try testing your user-defined
function in a stand alone test program first.
function in a stand-alone test program first.
5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
alloc set!" mean?