View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000070 | Pgpool-II | Bug | public | 2013-09-04 00:03 | 2013-10-19 14:01 |
| Reporter | glenngerhardt | Assigned To | t-ishii | ||
| Priority | normal | Severity | major | Reproducibility | always |
| Status | resolved | Resolution | open | ||
| OS | Centos | OS Version | 6.3 | ||
| Summary | 0000070: on memory caching can fill up, expired items not purged. | ||||
| Description | When the number of elements that can be cached is depleted, caching of new items will cease. There are multiple expired cache items that could be purged to make room for the new cache items, but purging of expired items only occurs when free memory is depleted. Increasing the value of memqcache_max_num_cache may help, but if this value is reached prior to reaching memqcache_total_size then caching of new entries will stop working and purging of old items will never happen. pool_hash_insert() will check to see if enough memory is available to insert the item. There is enough memory, so there is no purge of old items in the cache. Then later in pool_hash_insert() it will call get_new_has_element() which will fail due to being out of elements. This log is seen at that time: pool_hash_insert: could not get new element To fix this: purge old expired cache entries when memqcache_max_num_cache is hit. | ||||
| Steps To Reproduce | Easily reproduced when you lower the memqcache_max_num_cache value to a small number such as 1024, but keep the memqcache_total_size a large value. Populate the cache with items. When it attemps to cache the 1025th item, it will fail. As the 1024 items in cache expire, they are never purged out. I've seen the scenario occur with higher values, but lowering this makes repro quicker. Running with the inverse config (large memqcache_max_num and small memqcache_total_size) will show that expired cache items are purged to make room when free memory is depleted. | ||||
| Additional Information | pgpool.conf parameters: memory_cache_enabled = on memqcache_method = 'shmem' memqcache_total_size = 1073741824 memqcache_max_num_cache = 1048576 memqcache_expire = 10 memqcache_auto_cache_invalidation = on memqcache_maxcache = 409600 memqcache_cache_block_size = 1048576 white_memqcache_table_list = '' black_memqcache_table_list = '' memqcache_oiddir = '/dev/shm/pgpool/oiddir' | ||||
| Tags | No tags attached. | ||||
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You are right. Before insert a new cache entry, pgpool-II should make sure that there's at least one usable hash element. Included patch should do the trick. Note that it does not purge expired cache entry, rather look for next victim cache block because: 1) cache expiration is not always on 2) look for expired cache entry could be very expensive (there could be huge number of cache entries). Note that the patch is for git master head. But should be applied to V3.3 or V3.2 with something like: patch -p 3 |
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This change appears to be working. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2013-09-04 00:03 | glenngerhardt | New Issue | |
| 2013-09-04 09:48 | t-ishii | Assigned To | => t-ishii |
| 2013-09-04 09:48 | t-ishii | Status | new => assigned |
| 2013-09-04 13:36 | t-ishii | Note Added: 0000319 | |
| 2013-09-04 13:36 | t-ishii | File Added: poool_memqcache.c.patch | |
| 2013-09-04 13:36 | t-ishii | Status | assigned => feedback |
| 2013-10-17 07:07 | glenngerhardt | Note Added: 0000347 | |
| 2013-10-17 07:07 | glenngerhardt | Status | feedback => assigned |
| 2013-10-19 13:18 | t-ishii | Status | assigned => resolved |
| 2013-10-19 14:01 | t-ishii | Changeset attached | => pgpool2 master d6c447df |
