'\" t
.\"     Title: SHOW POOL_CACHE
.\"    Author: The Pgpool Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 2023
.\"    Manual: pgpool-II 4.3.7 Documentation
.\"    Source: pgpool-II 4.3.7
.\"  Language: English
.\"
.TH "SHOW POOL_CACHE" "1" "2023" "pgpool-II 4.3.7" "pgpool-II 4.3.7 Documentation"
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.SH "NAME"
SHOW_POOL_CACHE \- displays cache storage statistics
.SH "SYNOPSIS"
.sp
.nf
   SHOW POOL_CACHE
  
.fi
.SH "DESCRIPTION"
.PP
\fBSHOW POOL_CACHE\fR
displays
in memory query cache
statistics if in memory query cache is enabled\&. Here is an example session: See
Table\ \&26, \(lqItems displayed in show pool_cache\(rq
for a description of each item\&.
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.if n \{\
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.nf
    test=# \ex
    \ex
    Expanded display is on\&.
    test=# show pool_cache;
    show pool_cache;
    \-[ RECORD 1 ]\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-+\-\-\-\-\-\-\-\-\-
    num_cache_hits              | 891703
    num_selects                 | 99995
    cache_hit_ratio             | 0\&.90
    num_hash_entries            | 131072
    used_hash_entries           | 99992
    num_cache_entries           | 99992
    used_cache_entries_size     | 12482600
    free_cache_entries_size     | 54626264
    fragment_cache_entries_size | 0
   
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\fBNote\fR
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.br
.PP
If the cache storage is memcached, values for all columns except num_cache_hits, num_selects and cache_hit_ratio show 0\&.
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.RE
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.br
.B Table\ \&26.\ \&Items displayed in show pool_cache
.TS
allbox tab(:);
lB lB.
T{
Name
T}:T{
Description
T}
.T&
l l
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l l.
T{
num_cache_hits
T}:T{
The number of hits against the query cache\&.
T}
T{
num_selects
T}:T{
The number of SELECT that did not hit against the query cache\&.
T}
T{
cache_hit_ratio
T}:T{
The cache hit ratio\&.
       Calculated as num_cache_hits/(num_cache_hits+num_selects)\&.
T}
T{
num_hash_entries
T}:T{
The number of entries in the hash table used to manage
       the cache\&.  In order to manage large number of
       cache Pgpool\-II uses the hash table\&.
       The number of hash entries is automatically adjusted to the
       nearest power of two greater
       than memqcache_max_num_cache\&.  For
       example, 100,000, which is the default
       for memqcache_max_num_cache is adjusted to
       131,072 (2 to the 17th power)\&.
T}
T{
used_hash_entries
T}:T{
The number of used hash entries\&.  If the value
       approaches num_hash_entries, it is
       recommended to increase num_hash_entries\&.
       Even if all the hash table entries are used, no error is
       raised\&.  However, performance suffers because hash table
       entries and caches are reused to register new cache entries\&.
T}
T{
num_cache_entries
T}:T{
The number of cache entries already used\&.  In the current
       implementation the number should be identical
       to used_hash_entries\&.
T}
T{
free_cache_entries_size
T}:T{
The size in bytes of the unsed cache\&.  As this value approaches
       0, it removes the registered cache and registers a new cache,
       which does not cause an error, but reduces performance\&.
       Consider to increase memqcache_total_size\&.
T}
T{
fragment_cache_entries_size
T}:T{
The size in bytes of the fragmented cache\&.  When a registered
       cache is evicted, the space becomes fragmented until the next
       time that block is reused\&.
       Pgpool\-II writes cache in fixed\-size
	blocks specified
	by memqcache_cache_block_size\&.  When a
	registered cache is evicted, the space becomes fragmented
	until the next time that block is reused\&.
	fragment_cache_entries_size displays the
	total size of such fragmented regions\&.
T}
.TE
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