Laszlo Csontos created JCR-3453:
-----------------------------------
Summary: Jackrabbit might deplate the temporary tablespace on
Oracle
Key: JCR-3453
URL: https://issues.apache.org/jira/browse/JCR-3453
Project: Jackrabbit Content Repository
Issue Type: Bug
Affects Versions: 2.5.2, 2.1.2
Environment: Operating system: Linux
Application server: Websphere v7
RDBMS: Oracle 11g
Jackrabbit: V2.1.2 (built into Liferay 6.0 EE SP2)
Reporter: Laszlo Csontos
*** Experienced phenomenon ***
Our customer reported an issue regarding Liferay’s document library: while
documents are being retrieved, the following exception occurs accompanied by
temporary tablespace shortage.
[9/24/12 8:00:55:973 CEST] 00000023 SystemErr R ERROR
[org.apache.jackrabbit.core.util.db.ConnectionHelper:454] Failed to execute SQL
(stacktrace on DEBUG log level)
java.sql.SQLException: ORA-01652: unable to extend temp segment by 128 in
tablespace TEMP
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:440)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:396)
…
at
oracle.jdbc.driver.OraclePreparedStatementWrapper.execute(OraclePreparedStatementWrapper.java:1374)
at
com.ibm.ws.rsadapter.jdbc.WSJdbcPreparedStatement.pmiExecute(WSJdbcPreparedStatement.java:928)
at
com.ibm.ws.rsadapter.jdbc.WSJdbcPreparedStatement.execute(WSJdbcPreparedStatement.java:614)
…
at
org.apache.jackrabbit.core.util.db.ConnectionHelper.exec(ConnectionHelper.java:328)
at
org.apache.jackrabbit.core.fs.db.DatabaseFileSystem.getInputStream(DatabaseFileSystem.java:663)
at
org.apache.jackrabbit.core.fs.BasedFileSystem.getInputStream(BasedFileSystem.java:121)
at
org.apache.jackrabbit.core.fs.FileSystemResource.getInputStream(FileSystemResource.java:149)
at
org.apache.jackrabbit.core.RepositoryImpl.loadRootNodeId(RepositoryImpl.java:556)
at org.apache.jackrabbit.core.RepositoryImpl.<init>(RepositoryImpl.java:325)
at org.apache.jackrabbit.core.RepositoryImpl.create(RepositoryImpl.java:673)
at
org.apache.jackrabbit.core.TransientRepository$2.getRepository(TransientRepository.java:231)
at
org.apache.jackrabbit.core.TransientRepository.startRepository(TransientRepository.java:279)
at
org.apache.jackrabbit.core.TransientRepository.login(TransientRepository.java:375)
at
com.liferay.portal.jcr.jackrabbit.JCRFactoryImpl.createSession(JCRFactoryImpl.java:67)
at com.liferay.portal.jcr.JCRFactoryUtil.createSession(JCRFactoryUtil.java:43)
at com.liferay.portal.jcr.JCRFactoryUtil.createSession(JCRFactoryUtil.java:47)
at com.liferay.documentlibrary.util.JCRHook.getFileAsStream(JCRHook.java:472)
at
com.liferay.documentlibrary.util.HookProxyImpl.getFileAsStream(HookProxyImpl.java:149)
at
com.liferay.documentlibrary.util.SafeFileNameHookWrapper.getFileAsStream(SafeFileNameHookWrapper.java:236)
at
com.liferay.documentlibrary.service.impl.DLLocalServiceImpl.getFileAsStream(DLLocalServiceImpl.java:192)
The original size of tablespace TEMP used to be 8Gb when the error has occurred
for the first time. Later on it was extended by as much as additional 7Gb to
15Gb, yet the available space was still not sufficient to fulfill subsequent
requests and ORA-01652 emerged again.
*** Reproduction steps ***
1) Create a dummy 10MB file
$ dd if=/dev/urandom of=/path/to/dummy_blob bs=8192 count=1280
1280+0 records in
1280+0 records out
10485760 bytes (10 MB) copied, 0.722818 s, 14.5 MB/s
2) Create a temp tablespace
The tablespace is created with 5Mb and automatic expansion is intentionally
disabled.
SQL> CREATE TEMPORARY TABLESPACE jcr_temp
TEMPFILE '/path/to/jcr_temp_01.dbf'
SIZE 5M AUTOEXTEND OFF;
Table created.
SQL> ALTER USER jcr TEMPORARY TABLESPACE jcr_temp;
User altered.
3) Prepare the test case
For the sake of simplicity a dummy table is created (similar to Jackrabbit's
FSENTRY).
SQL> create table FSENTRY(data blob);
Table created.
SQL>
CREATE OR REPLACE PROCEDURE load_blob
AS
dest_loc BLOB;
src_loc BFILE := BFILENAME('DATA_PUMP_DIR', 'dummy_blob');
BEGIN
INSERT INTO FSENTRY (data)
VALUES (empty_blob())
RETURNING data INTO dest_loc;
DBMS_LOB.OPEN(src_loc, DBMS_LOB.LOB_READONLY);
DBMS_LOB.OPEN(dest_loc, DBMS_LOB.LOB_READWRITE);
DBMS_LOB.LOADFROMFILE(
dest_lob => dest_loc
, src_lob => src_loc
, amount => DBMS_LOB.getLength(src_loc));
DBMS_LOB.CLOSE(dest_loc);
DBMS_LOB.CLOSE(src_loc);
COMMIT;
END;
/
Procedure created.
SQL> EXEC load_blob();
PL/SQL procedure successfully completed.
4) Execute the query
SQL> select nvl(data, empty_blob()) from FSENTRY;
ERROR: ORA-01652: unable to extend temp segment by 128 in tablespace JCR_TEMP
4) Let’s see how temporary tablespace is being used
Query the size of the original LOB data.
SELECT s.segment_name,
s.segment_type,
SUM(s.blocks) AS blocks
FROM dba_segments s,
(SELECT segment_name, index_name
FROM dba_lobs l
WHERE l.table_name = 'FSENTRY'
AND l.column_name = 'DATA') ls
WHERE s.segment_name = ls.segment_name
OR s.segment_name = ls.index_name
GROUP BY s.segment_name, s.segment_type;
SEGMENT_NAME SEGMENT_TYPE BLOCKS
---------------------------------------------------------------------------
SYS_LOB0000035993C00001$$ LOBSEGMENT 1408
SYS_IL0000035993C00001$$ LOBINDEX 8
Query the size of the temporarily created LOB data.
SELECT s.sql_text, t.segtype, t.blocks
FROM v$sql s, v$tempseg_usage t
WHERE s.sql_id = t.sql_id;
SQL_TEXT SEGTYPE BLOCKS
---------------------------------------------------------------------------
select nvl(data, empty_blob()) from lobtest LOB_DATA 1408 (~11 Mb)
select nvl(data, empty_blob()) from lobtest LOB_INDEX 128 (~1 Mb)
LOB index might need some explanation: it's an internal structure that is
strongly associated with LOB storage (LOB locators point to the top of the LOB
index tree, where leaf blocks point to the actual LOB chunks). The bottom line
is that a user may not drop/alter/rebuild LOB indexes in any way.
As a conclusion we can see here that a temporary LOB has been been created by
Oracle indeed and its space requirements are quite similar to the original one.
*** Analysis ***
The aforementioned exception is thrown in the getInputStream(...) method of
class org.apache.jackrabbit.core.fs.db.DatabaseFileSystem while it’s attempting
to execute that SQL statement which is denoted by selectDataSQL.
Based on this particular case, customer has the Jackrabbit repository
configured to use org.apache.jackrabbit.core.fs.db.OracleFileSystem, which
implies that the actual value of selectDataSQL is the following.
SELECT NVL(FSENTRY_DATA, empty_blob())
FROM J_FSASSSA_1LIFERAYFSENTRY
WHERE FSENTRY_PATH = :1
AND FSENTRY_NAME = :2
AND FSENTRY_LENGTH IS NOT NULL
The most important point here is that Oracle creates temporary LOBs, if LOB
columns are used in SQL functions. From the point of view of Oracle, it’s a
completely logical behaviour, since it has to evaluate the given expression and
during doing so the database manager also has to store the result of that
calculation.
In this case, if column FSENTRY_DATA is null an empty LOB locator is created,
however it’s unclear why it is functionally required. Interestingly other
database file system implementations (eg. for DB2) do not use an equivalent SQL
function at the same place (eg. COALSCE in case of DB2), but they return
FSENTRY_DATA directly without performing such a pre-processing.
The second part of the experienced problem is that according to the Oracle 11g
Database SecureFiles and Large Objects Developer's Guide, if a temporary LOB
has been returned to the application, it’s the caller (except PL/SQL program
blocks) responsibility to explicitly free the received object. Having this in
mind, handling temporary LOBs in a decent way can be accomplished by checking
and freeing them manually.
void someMethod() {
...
ResultSet rs = ...
oracle.sql.BLOB data = (oracle.sql.BLOB) rs.getBlob(...);
if (data.isTemporary()) {
data.freeTemporary();
}
...
}
Apparently org.apache.jackrabbit.core.fs.db.OracleFileSystem does not take care
of disposing temporary LOBs and temporary tablespace is being depleted this way
in a long run.
*** Conclusion ***
Jackrabbit definitely should at least free temporary LOBs in OracleFileSystem
or avoid using the NVL function completely and moving that logic to the
application instead, would make the whole phenomenon cease to exist.
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