DB2 - Problem description
Problem IT33488 | Status: Closed |
Queries might hang in UOW-Exec waiting on SQLO_LT_SQLB_HASH_BUCKET_GROUP_HEADER__groupLatch in sqlbFindPageInBPOrSim function | |
product: | |
DB2 FOR LUW / DB2FORLUW / B50 - DB2 | |
Problem description: | |
Under rare timing conditions, with high concurrency, queries might get stuck in UOW-Executing state with the following function on the top of the stack of the coordinator agent (db2agent EDU) SQLO_SLATCH_CAS64::getConflict sqlbFindPageInBPOrSim sqlbfix At the same time, multiple prefetcehrs (db2pfchr EDUs) will be show waiting in: SQLO_SLATCH_CAS64::getConflict sqlbFindPageInBPForPrefetch sqlbGetBuffer sqlbProcessRange sqlbPFPrefetcherEntryPoint and one db2agent with sqlbRemovePageFromSimulationArea function on the stack: SQLO_SLATCH_CAS64::getConflict sqlbRemovePageFromSimulationArea sqlbFindPageInBPOrSim sqlbfix db2pd -latches will report multiple waiters on the same SQLO_LT_SQLB_HASH_BUCKET_GROUP_HEADER__groupLatch address, with the latch holder EDU ID changing across iterations. MON_GET_LATCH query, e.g.: select substr(latch_name,1,40) latch_name, substr(memory_address,1,20) memory_address, edu_id, substr(edu_name,1,20) edu_name, application_handle, member, latch_status, latch_wait_time from table ( mon_get_latch( null, -2 ) ) where latch_status = 'W' order by latch_wait_time might show at least one EDU_ID waiting on that latch address for significant amount of time. Problem is specific to databases where size of bufferpool(s) is controlled by STMM (SIZE AUTOMATIC) and it is more likely to be exposed on systems with large number of CPUs, very large bufferpool and under a heavy prefetch activity. | |
Problem Summary: | |
**************************************************************** * USERS AFFECTED: * * ALL * **************************************************************** * PROBLEM DESCRIPTION: * * See Error Description * **************************************************************** * RECOMMENDATION: * * Update to Db2 version 11.1 Mod 4 Fix Pack 6 or newer. * **************************************************************** | |
Local Fix: | |
Disable self tuning for bufferpools: ALTER BUFFERPOOL SIZE | |
Solution | |
Workaround | |
Disable self tuning for bufferpools: ALTER BUFFERPOOL SIZE | |
BUG-Tracking | |
forerunner : follow-up : IT33546 | |
Timestamps | |
Date - problem reported : Date - problem closed : Date - last modified : | 09.07.2020 26.11.2020 26.11.2020 |
Problem solved at the following versions (IBM BugInfos) | |
Problem solved according to the fixlist(s) of the following version(s) |