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Diffstat (limited to 'doc/FAQ')
| -rw-r--r-- | doc/FAQ | 60 |
1 files changed, 39 insertions, 21 deletions
@@ -1,7 +1,7 @@ Frequently Asked Questions (FAQ) for PostgreSQL - Last updated: Sat Jul 10 00:37:57 EDT 1999 + Last updated: Wed Sep 1 19:26:40 EDT 1999 Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us) @@ -49,7 +49,7 @@ 3.2) How do I install PostgreSQL somewhere other than /usr/local/pgsql? 3.3) When I start the postmaster, I get a Bad System Call or core - dumped message3. Why? + dumped message. Why? 3.4) When I try to start the postmaster, I get IpcMemoryCreate errors3. Why? 3.5) When I try to start the postmaster, I get IpcSemaphoreCreate @@ -93,6 +93,8 @@ 4.19) Why do I get the error "FATAL: palloc failure: memory exhausted?" 4.20) How do I tell what PostgreSQL version I am running? + 4.21) My large-object operations get invalid large obj descriptor. + Why? Extending PostgreSQL @@ -213,7 +215,6 @@ available for discussion of matters pertaining to PostgreSQL. To subscribe, send a mail with the lines in the body (not the subject line) - subscribe end @@ -221,7 +222,6 @@ There is also a digest list available. To subscribe to this list, send email to: pgsql-general-digest-request@postgreSQL.org with a BODY of: - subscribe end @@ -231,7 +231,6 @@ The bugs mailing list is available. To subscribe to this list, send email to bugs-request@postgreSQL.org with a BODY of: - subscribe end @@ -239,7 +238,6 @@ subscribe to this list, send email to hackers-request@postgreSQL.org with a BODY of: - subscribe end @@ -315,9 +313,9 @@ Features PostgreSQL has most features present in large commercial - DBMS's, like transactions, subselects, and sophisticated - locking. We have some features they don't have, like - user-defined types, inheritance, rules, and multi-version + DBMS's, like transactions, subselects, triggers, views, and + sophisticated locking. We have some features they don't have, + like user-defined types, inheritance, rules, and multi-version concurrency control to reduce lock contention. We don't have foreign key referential integrity or outer joins, but are working on them for our next release. @@ -325,21 +323,26 @@ Performance PostgreSQL runs in two modes. Normal fsync mode flushes every completed transaction to disk, guaranteeing that if the OS - crashes or looses power in the next few seconds, all your data + crashes or loses power in the next few seconds, all your data is safely stored on disk. In this mode, we are slower than most commercial databases, partly because few of them do such conservative flushing to disk in their default modes. In no-fsync mode, we are usually faster than commercial databases, though in this mode, an OS crash could cause data corruption. We are working to provide an intermediate mode that suffers - from less performance overhead than full fsync mode, and will - allow data integrity within 30 seconds of an OS crash. The mode - is select-able by the database administrator. - + less performance overhead than full fsync mode, and will allow + data integrity within 30 seconds of an OS crash. The mode is + select-able by the database administrator. In comparison to MySQL or leaner database systems, we are - slower because we have transaction overhead. We are built for - flexibility and features, not speed, though we continue to - improve performance through profiling and source code analysis. + slower on inserts/updates because we have transaction overhead. + Of course, MySQL doesn't have any of the features mentioned in + the Features section above. We are built for flexibility and + features, though we continue to improve performance through + profiling and source code analysis. + We handle each user connection by creating a Unix process. + Backend processes share data buffers and locking information. + With multiple CPU's, multiple backends can easily run on + different CPU's. Reliability We realize that a DBMS must be reliable, or it is worthless. We @@ -544,7 +547,6 @@ Both postmaster and postgres have several debug options available. First, whenever you start the postmaster, make sure you send the standard output and error to a log file, like: - cd /usr/local/pgsql ./bin/postmaster >server.log 2>&1 & @@ -615,7 +617,6 @@ Currently, there is no easy interface to set up user groups. You have to explicitly insert/update the pg_group table. For example: - jolly=> insert into pg_group (groname, grosysid, grolist) jolly=> values ('posthackers', '1234', '{5443, 8261}'); INSERT 548224 @@ -667,7 +668,6 @@ 4.5) How do you remove a column from a table? We do not support alter table drop column, but do this: - SELECT ... -- select all columns but the one you want to remove INTO TABLE new_table FROM old_table; @@ -871,7 +871,6 @@ BYTEA bytea variable-length array of bytes It is possible you have run out of virtual memory on your system, or your kernel has a low limit for certain resources. Try this before starting the postmaster: - ulimit -d 65536 limit datasize 64m @@ -885,6 +884,25 @@ BYTEA bytea variable-length array of bytes 4.20) How do I tell what PostgreSQL version I am running? From psql, type select version(); + + 4.21) My large-object operations get invalid large obj descriptor. Why? + + You need to put BEGIN WORK and COMMIT around any use of a large object + handle, that is, surrounding lo_open ... lo_close. + + The documentation has always stated that lo_open must be wrapped in a + transaction, but PostgreSQL versions prior to 6.5 didn't enforce that + rule. Instead, they'd just fail occasionally if you broke it. + + Current PostgreSQL enforces the rule by closing large object handles + at transaction commit, which will be instantly upon completion of the + lo_open command if you are not inside a transaction. So the first + attempt to do anything with the handle will draw invalid large obj + descriptor. So code that used to work (at least most of the time) will + now generate that error message if you fail to use a transaction. + + If you are using a client interface like ODBC you may need to set + auto-commit off. _________________________________________________________________ Extending PostgreSQL |